/*

 ** 2001 September 15

 **

 ** The author disclaims copyright to this source code.  In place of

 ** a legal notice, here is a blessing:

 **

 **    May you do good and not evil.

 **    May you find forgiveness for yourself and forgive others.

 **    May you share freely, never taking more than you give.

 **

 *************************************************************************

 ** This module contains C code that generates VDBE code used to process

 ** the WHERE clause of SQL statements.  This module is responsible for

 ** generating the code that loops through a table looking for applicable

 ** rows.  Indices are selected and used to speed the search when doing

 ** so is applicable.  Because this module is responsible for selecting

 ** indices, you might also think of this module as the "query optimizer".

 **

 ** $Id: where.c,v 1.319 2008/08/01 17:37:41 danielk1977 Exp $

 */

 #include "sqliteInt.h"

 /*

 ** The number of bits in a Bitmask.  "BMS" means "BitMask Size".

 */

 #define BMS  (sizeof(Bitmask)*8)

 /*

 ** Trace output macros

 */

 #if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)

 int sqlite3WhereTrace = 0;

 #endif

 #if 0

 # define WHERETRACE(X)  if(sqlite3WhereTrace) sqlite3DebugPrintf X

 #else

 # define WHERETRACE(X)

 #endif

 /* Forward reference

 */

 typedef struct WhereClause WhereClause;

 typedef struct ExprMaskSet ExprMaskSet;

 /*

 ** The query generator uses an array of instances of this structure to

 ** help it analyze the subexpressions of the WHERE clause.  Each WHERE

 ** clause subexpression is separated from the others by an AND operator.

 **

 ** All WhereTerms are collected into a single WhereClause structure.  

 ** The following identity holds:

 **

 **        WhereTerm.pWC->a[WhereTerm.idx] == WhereTerm

 **

 ** When a term is of the form:

 **

 **              X <op> <expr>

 **

 ** where X is a column name and <op> is one of certain operators,

 ** then WhereTerm.leftCursor and WhereTerm.leftColumn record the

 ** cursor number and column number for X.  WhereTerm.operator records

 ** the <op> using a bitmask encoding defined by WO_xxx below.  The

 ** use of a bitmask encoding for the operator allows us to search

 ** quickly for terms that match any of several different operators.

 **

 ** prereqRight and prereqAll record sets of cursor numbers,

 ** but they do so indirectly.  A single ExprMaskSet structure translates

 ** cursor number into bits and the translated bit is stored in the prereq

 ** fields.  The translation is used in order to maximize the number of

 ** bits that will fit in a Bitmask.  The VDBE cursor numbers might be

 ** spread out over the non-negative integers.  For example, the cursor

 ** numbers might be 3, 8, 9, 10, 20, 23, 41, and 45.  The ExprMaskSet

 ** translates these sparse cursor numbers into consecutive integers

 ** beginning with 0 in order to make the best possible use of the available

 ** bits in the Bitmask.  So, in the example above, the cursor numbers

 ** would be mapped into integers 0 through 7.

 */

 typedef struct WhereTerm WhereTerm;

 struct WhereTerm {

   Expr *pExpr;            /* Pointer to the subexpression */

   i16 iParent;            /* Disable pWC->a[iParent] when this term disabled */

   i16 leftCursor;         /* Cursor number of X in "X <op> <expr>" */

   i16 leftColumn;         /* Column number of X in "X <op> <expr>" */

   u16 eOperator;          /* A WO_xx value describing <op> */

   u8 flags;               /* Bit flags.  See below */

   u8 nChild;              /* Number of children that must disable us */

   WhereClause *pWC;       /* The clause this term is part of */

   Bitmask prereqRight;    /* Bitmask of tables used by pRight */

   Bitmask prereqAll;      /* Bitmask of tables referenced by p */

 };

 /*

 ** Allowed values of WhereTerm.flags

 */

 #define TERM_DYNAMIC    0x01   /* Need to call sqlite3ExprDelete(db, pExpr) */

 #define TERM_VIRTUAL    0x02   /* Added by the optimizer.  Do not code */

 #define TERM_CODED      0x04   /* This term is already coded */

 #define TERM_COPIED     0x08   /* Has a child */

 #define TERM_OR_OK      0x10   /* Used during OR-clause processing */

 /*

 ** An instance of the following structure holds all information about a

 ** WHERE clause.  Mostly this is a container for one or more WhereTerms.

 */

 struct WhereClause {

   Parse *pParse;           /* The parser context */

   ExprMaskSet *pMaskSet;   /* Mapping of table indices to bitmasks */

   int nTerm;               /* Number of terms */

   int nSlot;               /* Number of entries in a[] */

   WhereTerm *a;            /* Each a[] describes a term of the WHERE cluase */

   WhereTerm aStatic[10];   /* Initial static space for a[] */

 };

 /*

 ** An instance of the following structure keeps track of a mapping

 ** between VDBE cursor numbers and bits of the bitmasks in WhereTerm.

 **

 ** The VDBE cursor numbers are small integers contained in 

 ** SrcList_item.iCursor and Expr.iTable fields.  For any given WHERE 

 ** clause, the cursor numbers might not begin with 0 and they might

 ** contain gaps in the numbering sequence.  But we want to make maximum

 ** use of the bits in our bitmasks.  This structure provides a mapping

 ** from the sparse cursor numbers into consecutive integers beginning

 ** with 0.

 **

 ** If ExprMaskSet.ix[A]==B it means that The A-th bit of a Bitmask

 ** corresponds VDBE cursor number B.  The A-th bit of a bitmask is 1<<A.

 **

 ** For example, if the WHERE clause expression used these VDBE

 ** cursors:  4, 5, 8, 29, 57, 73.  Then the  ExprMaskSet structure

 ** would map those cursor numbers into bits 0 through 5.

 **

 ** Note that the mapping is not necessarily ordered.  In the example

 ** above, the mapping might go like this:  4->3, 5->1, 8->2, 29->0,

 ** 57->5, 73->4.  Or one of 719 other combinations might be used. It

 ** does not really matter.  What is important is that sparse cursor

 ** numbers all get mapped into bit numbers that begin with 0 and contain

 ** no gaps.

 */

 struct ExprMaskSet {

   int n;                        /* Number of assigned cursor values */

   int ix[sizeof(Bitmask)*8];    /* Cursor assigned to each bit */

 };

 /*

 ** Bitmasks for the operators that indices are able to exploit.  An

 ** OR-ed combination of these values can be used when searching for

 ** terms in the where clause.

 */

 #define WO_IN     1

 #define WO_EQ     2

 #define WO_LT     (WO_EQ<<(TK_LT-TK_EQ))

 #define WO_LE     (WO_EQ<<(TK_LE-TK_EQ))

 #define WO_GT     (WO_EQ<<(TK_GT-TK_EQ))

 #define WO_GE     (WO_EQ<<(TK_GE-TK_EQ))

 #define WO_MATCH  64

 #define WO_ISNULL 128

 /*

 ** Value for flags returned by bestIndex().  

 **

 ** The least significant byte is reserved as a mask for WO_ values above.

 ** The WhereLevel.flags field is usually set to WO_IN|WO_EQ|WO_ISNULL.

 ** But if the table is the right table of a left join, WhereLevel.flags

 ** is set to WO_IN|WO_EQ.  The WhereLevel.flags field can then be used as

 ** the "op" parameter to findTerm when we are resolving equality constraints.

 ** ISNULL constraints will then not be used on the right table of a left

 ** join.  Tickets #2177 and #2189.

 */

 #define WHERE_ROWID_EQ     0x000100   /* rowid=EXPR or rowid IN (...) */

 #define WHERE_ROWID_RANGE  0x000200   /* rowid<EXPR and/or rowid>EXPR */

 #define WHERE_COLUMN_EQ    0x001000   /* x=EXPR or x IN (...) */

 #define WHERE_COLUMN_RANGE 0x002000   /* x<EXPR and/or x>EXPR */

 #define WHERE_COLUMN_IN    0x004000   /* x IN (...) */

 #define WHERE_TOP_LIMIT    0x010000   /* x<EXPR or x<=EXPR constraint */

 #define WHERE_BTM_LIMIT    0x020000   /* x>EXPR or x>=EXPR constraint */

 #define WHERE_IDX_ONLY     0x080000   /* Use index only - omit table */

 #define WHERE_ORDERBY      0x100000   /* Output will appear in correct order */

 #define WHERE_REVERSE      0x200000   /* Scan in reverse order */

 #define WHERE_UNIQUE       0x400000   /* Selects no more than one row */

 #define WHERE_VIRTUALTABLE 0x800000   /* Use virtual-table processing */

 /*

 ** Initialize a preallocated WhereClause structure.

 */

 static void whereClauseInit(

   WhereClause *pWC,        /* The WhereClause to be initialized */

   Parse *pParse,           /* The parsing context */

   ExprMaskSet *pMaskSet    /* Mapping from table indices to bitmasks */

 ){

   pWC->pParse = pParse;

   pWC->pMaskSet = pMaskSet;

   pWC->nTerm = 0;

   pWC->nSlot = ArraySize(pWC->aStatic);

   pWC->a = pWC->aStatic;

 }

 /*

 ** Deallocate a WhereClause structure.  The WhereClause structure

 ** itself is not freed.  This routine is the inverse of whereClauseInit().

 */

 static void whereClauseClear(WhereClause *pWC){

   int i;

   WhereTerm *a;

   sqlite3 *db = pWC->pParse->db;

   for(i=pWC->nTerm-1, a=pWC->a; i>=0; i--, a++){

     if( a->flags & TERM_DYNAMIC ){

       sqlite3ExprDelete(db, a->pExpr);

     }

   }

   if( pWC->a!=pWC->aStatic ){

     sqlite3DbFree(db, pWC->a);

   }

 }

 /*

 ** Add a new entries to the WhereClause structure.  Increase the allocated

 ** space as necessary.

 **

 ** If the flags argument includes TERM_DYNAMIC, then responsibility

 ** for freeing the expression p is assumed by the WhereClause object.

 **

 ** WARNING:  This routine might reallocate the space used to store

 ** WhereTerms.  All pointers to WhereTerms should be invalidated after

 ** calling this routine.  Such pointers may be reinitialized by referencing

 ** the pWC->a[] array.

 */

 static int whereClauseInsert(WhereClause *pWC, Expr *p, int flags){

   WhereTerm *pTerm;

   int idx;

   if( pWC->nTerm>=pWC->nSlot ){

     WhereTerm *pOld = pWC->a;

     sqlite3 *db = pWC->pParse->db;

     pWC->a = sqlite3DbMallocRaw(db, sizeof(pWC->a[0])*pWC->nSlot*2 );

     if( pWC->a==0 ){

       if( flags & TERM_DYNAMIC ){

         sqlite3ExprDelete(db, p);

       }

       pWC->a = pOld;

       return 0;

     }

     memcpy(pWC->a, pOld, sizeof(pWC->a[0])*pWC->nTerm);

     if( pOld!=pWC->aStatic ){

       sqlite3DbFree(db, pOld);

     }

     pWC->nSlot *= 2;

   }

   pTerm = &pWC->a[idx = pWC->nTerm];

   pWC->nTerm++;

   pTerm->pExpr = p;

   pTerm->flags = flags;

   pTerm->pWC = pWC;

   pTerm->iParent = -1;

   return idx;

 }

 /*

 ** This routine identifies subexpressions in the WHERE clause where

 ** each subexpression is separated by the AND operator or some other

 ** operator specified in the op parameter.  The WhereClause structure

 ** is filled with pointers to subexpressions.  For example:

 **

 **    WHERE  a=='hello' AND coalesce(b,11)<10 AND (c+12!=d OR c==22)

 **           \________/     \_______________/     \________________/

 **            slot[0]            slot[1]               slot[2]

 **

 ** The original WHERE clause in pExpr is unaltered.  All this routine

 ** does is make slot[] entries point to substructure within pExpr.

 **

 ** In the previous sentence and in the diagram, "slot[]" refers to

 ** the WhereClause.a[] array.  This array grows as needed to contain

 ** all terms of the WHERE clause.

 */

 static void whereSplit(WhereClause *pWC, Expr *pExpr, int op){

   if( pExpr==0 ) return;

   if( pExpr->op!=op ){

     whereClauseInsert(pWC, pExpr, 0);

   }else{

     whereSplit(pWC, pExpr->pLeft, op);

     whereSplit(pWC, pExpr->pRight, op);

   }

 }

 /*

 ** Initialize an expression mask set

 */

 #define initMaskSet(P)  memset(P, 0, sizeof(*P))

 /*

 ** Return the bitmask for the given cursor number.  Return 0 if

 ** iCursor is not in the set.

 */

 static Bitmask getMask(ExprMaskSet *pMaskSet, int iCursor){

   int i;

   for(i=0; i<pMaskSet->n; i++){

     if( pMaskSet->ix[i]==iCursor ){

       return ((Bitmask)1)<<i;

     }

   }

   return 0;

 }

 /*

 ** Create a new mask for cursor iCursor.

 **

 ** There is one cursor per table in the FROM clause.  The number of

 ** tables in the FROM clause is limited by a test early in the

 ** sqlite3WhereBegin() routine.  So we know that the pMaskSet->ix[]

 ** array will never overflow.

 */

 static void createMask(ExprMaskSet *pMaskSet, int iCursor){

   assert( pMaskSet->n < ArraySize(pMaskSet->ix) );

   pMaskSet->ix[pMaskSet->n++] = iCursor;

 }

 /*

 ** This routine walks (recursively) an expression tree and generates

 ** a bitmask indicating which tables are used in that expression

 ** tree.

 **

 ** In order for this routine to work, the calling function must have

 ** previously invoked sqlite3ExprResolveNames() on the expression.  See

 ** the header comment on that routine for additional information.

 ** The sqlite3ExprResolveNames() routines looks for column names and

 ** sets their opcodes to TK_COLUMN and their Expr.iTable fields to

 ** the VDBE cursor number of the table.  This routine just has to

 ** translate the cursor numbers into bitmask values and OR all

 ** the bitmasks together.

 */

 static Bitmask exprListTableUsage(ExprMaskSet*, ExprList*);

 static Bitmask exprSelectTableUsage(ExprMaskSet*, Select*);

 static Bitmask exprTableUsage(ExprMaskSet *pMaskSet, Expr *p){

   Bitmask mask = 0;

   if( p==0 ) return 0;

   if( p->op==TK_COLUMN ){

     mask = getMask(pMaskSet, p->iTable);

     return mask;

   }

   mask = exprTableUsage(pMaskSet, p->pRight);

   mask |= exprTableUsage(pMaskSet, p->pLeft);

   mask |= exprListTableUsage(pMaskSet, p->pList);

   mask |= exprSelectTableUsage(pMaskSet, p->pSelect);

   return mask;

 }

 static Bitmask exprListTableUsage(ExprMaskSet *pMaskSet, ExprList *pList){

   int i;

   Bitmask mask = 0;

   if( pList ){

     for(i=0; i<pList->nExpr; i++){

       mask |= exprTableUsage(pMaskSet, pList->a[i].pExpr);

     }

   }

   return mask;

 }

 static Bitmask exprSelectTableUsage(ExprMaskSet *pMaskSet, Select *pS){

   Bitmask mask = 0;

   while( pS ){

     mask |= exprListTableUsage(pMaskSet, pS->pEList);

     mask |= exprListTableUsage(pMaskSet, pS->pGroupBy);

     mask |= exprListTableUsage(pMaskSet, pS->pOrderBy);

     mask |= exprTableUsage(pMaskSet, pS->pWhere);

     mask |= exprTableUsage(pMaskSet, pS->pHaving);

     pS = pS->pPrior;

   }

   return mask;

 }

 /*

 ** Return TRUE if the given operator is one of the operators that is

 ** allowed for an indexable WHERE clause term.  The allowed operators are

 ** "=", "<", ">", "<=", ">=", and "IN".

 */

 static int allowedOp(int op){

   assert( TK_GT>TK_EQ && TK_GT<TK_GE );

   assert( TK_LT>TK_EQ && TK_LT<TK_GE );

   assert( TK_LE>TK_EQ && TK_LE<TK_GE );

   assert( TK_GE==TK_EQ+4 );

   return op==TK_IN || (op>=TK_EQ && op<=TK_GE) || op==TK_ISNULL;

 }

 /*

 ** Swap two objects of type T.

 */

 #define SWAP(TYPE,A,B) {TYPE t=A; A=B; B=t;}

 /*

 ** Commute a comparison operator.  Expressions of the form "X op Y"

 ** are converted into "Y op X".

 **

 ** If a collation sequence is associated with either the left or right

 ** side of the comparison, it remains associated with the same side after

 ** the commutation. So "Y collate NOCASE op X" becomes 

 ** "X collate NOCASE op Y". This is because any collation sequence on

 ** the left hand side of a comparison overrides any collation sequence 

 ** attached to the right. For the same reason the EP_ExpCollate flag

 ** is not commuted.

 */

 static void exprCommute(Expr *pExpr){

   u16 expRight = (pExpr->pRight->flags & EP_ExpCollate);

   u16 expLeft = (pExpr->pLeft->flags & EP_ExpCollate);

   assert( allowedOp(pExpr->op) && pExpr->op!=TK_IN );

   SWAP(CollSeq*,pExpr->pRight->pColl,pExpr->pLeft->pColl);

   pExpr->pRight->flags = (pExpr->pRight->flags & ~EP_ExpCollate) | expLeft;

   pExpr->pLeft->flags = (pExpr->pLeft->flags & ~EP_ExpCollate) | expRight;

   SWAP(Expr*,pExpr->pRight,pExpr->pLeft);

   if( pExpr->op>=TK_GT ){

     assert( TK_LT==TK_GT+2 );

     assert( TK_GE==TK_LE+2 );

     assert( TK_GT>TK_EQ );

     assert( TK_GT<TK_LE );

     assert( pExpr->op>=TK_GT && pExpr->op<=TK_GE );

     pExpr->op = ((pExpr->op-TK_GT)^2)+TK_GT;

   }

 }

 /*

 ** Translate from TK_xx operator to WO_xx bitmask.

 */

 static int operatorMask(int op){

   int c;

   assert( allowedOp(op) );

   if( op==TK_IN ){

     c = WO_IN;

   }else if( op==TK_ISNULL ){

     c = WO_ISNULL;

   }else{

     c = WO_EQ<<(op-TK_EQ);

   }

   assert( op!=TK_ISNULL || c==WO_ISNULL );

   assert( op!=TK_IN || c==WO_IN );

   assert( op!=TK_EQ || c==WO_EQ );

   assert( op!=TK_LT || c==WO_LT );

   assert( op!=TK_LE || c==WO_LE );

   assert( op!=TK_GT || c==WO_GT );

   assert( op!=TK_GE || c==WO_GE );

   return c;

 }

 /*

 ** Search for a term in the WHERE clause that is of the form "X <op> <expr>"

 ** where X is a reference to the iColumn of table iCur and <op> is one of

 ** the WO_xx operator codes specified by the op parameter.

 ** Return a pointer to the term.  Return 0 if not found.

 */

 static WhereTerm *findTerm(

   WhereClause *pWC,     /* The WHERE clause to be searched */

   int iCur,             /* Cursor number of LHS */

   int iColumn,          /* Column number of LHS */

   Bitmask notReady,     /* RHS must not overlap with this mask */

   u16 op,               /* Mask of WO_xx values describing operator */

   Index *pIdx           /* Must be compatible with this index, if not NULL */

 ){

   WhereTerm *pTerm;

   int k;

   assert( iCur>=0 );

   for(pTerm=pWC->a, k=pWC->nTerm; k; k--, pTerm++){

     if( pTerm->leftCursor==iCur

        && (pTerm->prereqRight & notReady)==0

        && pTerm->leftColumn==iColumn

        && (pTerm->eOperator & op)!=0

     ){

       if( pIdx && pTerm->eOperator!=WO_ISNULL ){

         Expr *pX = pTerm->pExpr;

         CollSeq *pColl;

         char idxaff;

         int j;

         Parse *pParse = pWC->pParse;

         idxaff = pIdx->pTable->aCol[iColumn].affinity;

         if( !sqlite3IndexAffinityOk(pX, idxaff) ) continue;

         /* Figure out the collation sequence required from an index for

         ** it to be useful for optimising expression pX. Store this

         ** value in variable pColl.

         */

         assert(pX->pLeft);

         pColl = sqlite3BinaryCompareCollSeq(pParse, pX->pLeft, pX->pRight);

         if( !pColl ){

           pColl = pParse->db->pDfltColl;

         }

         for(j=0; pIdx->aiColumn[j]!=iColumn; j++){

           if( NEVER(j>=pIdx->nColumn) ) return 0;

         }

         if( sqlite3StrICmp(pColl->zName, pIdx->azColl[j]) ) continue;

       }

       return pTerm;

     }

   }

   return 0;

 }

 /* Forward reference */

 static void exprAnalyze(SrcList*, WhereClause*, int);

 /*

 ** Call exprAnalyze on all terms in a WHERE clause.  

 **

 **

 */

 static void exprAnalyzeAll(

   SrcList *pTabList,       /* the FROM clause */

   WhereClause *pWC         /* the WHERE clause to be analyzed */

 ){

   int i;

   for(i=pWC->nTerm-1; i>=0; i--){

     exprAnalyze(pTabList, pWC, i);

   }

 }

 #ifndef SQLITE_OMIT_LIKE_OPTIMIZATION

 /*

 ** Check to see if the given expression is a LIKE or GLOB operator that

 ** can be optimized using inequality constraints.  Return TRUE if it is

 ** so and false if not.

 **

 ** In order for the operator to be optimizible, the RHS must be a string

 ** literal that does not begin with a wildcard.  

 */

 static int isLikeOrGlob(

   sqlite3 *db,      /* The database */

   Expr *pExpr,      /* Test this expression */

   int *pnPattern,   /* Number of non-wildcard prefix characters */

   int *pisComplete, /* True if the only wildcard is % in the last character */

   int *pnoCase      /* True if uppercase is equivalent to lowercase */

 ){

   const char *z;

   Expr *pRight, *pLeft;

   ExprList *pList;

   int c, cnt;

   char wc[3];

   CollSeq *pColl;

   if( !sqlite3IsLikeFunction(db, pExpr, pnoCase, wc) ){

     return 0;

   }

 #ifdef SQLITE_EBCDIC

   if( *pnoCase ) return 0;

 #endif

   pList = pExpr->pList;

   pRight = pList->a[0].pExpr;

   if( pRight->op!=TK_STRING

    && (pRight->op!=TK_REGISTER || pRight->iColumn!=TK_STRING) ){

     return 0;

   }

   pLeft = pList->a[1].pExpr;

   if( pLeft->op!=TK_COLUMN ){

     return 0;

   }

   pColl = pLeft->pColl;

   assert( pColl!=0 || pLeft->iColumn==-1 );

   if( pColl==0 ){

     /* No collation is defined for the ROWID.  Use the default. */

     pColl = db->pDfltColl;

   }

   if( (pColl->type!=SQLITE_COLL_BINARY || *pnoCase) &&

       (pColl->type!=SQLITE_COLL_NOCASE || !*pnoCase) ){

     return 0;

   }

   sqlite3DequoteExpr(db, pRight);

   z = (char *)pRight->token.z;

   cnt = 0;

   if( z ){

     while( (c=z[cnt])!=0 && c!=wc[0] && c!=wc[1] && c!=wc[2] ){ cnt++; }

   }

   if( cnt==0 || 255==(u8)z[cnt] ){

     return 0;

   }

   *pisComplete = z[cnt]==wc[0] && z[cnt+1]==0;

   *pnPattern = cnt;

   return 1;

 }

 #endif /* SQLITE_OMIT_LIKE_OPTIMIZATION */

 #ifndef SQLITE_OMIT_VIRTUALTABLE

 /*

 ** Check to see if the given expression is of the form

 **

 **         column MATCH expr

 **

 ** If it is then return TRUE.  If not, return FALSE.

 */

 static int isMatchOfColumn(

   Expr *pExpr      /* Test this expression */

 ){

   ExprList *pList;

   if( pExpr->op!=TK_FUNCTION ){

     return 0;

   }

   if( pExpr->token.n!=5 ||

        sqlite3StrNICmp((const char*)pExpr->token.z,"match",5)!=0 ){

     return 0;

   }

   pList = pExpr->pList;

   if( pList->nExpr!=2 ){

     return 0;

   }

   if( pList->a[1].pExpr->op != TK_COLUMN ){

     return 0;

   }

   return 1;

 }

 #endif /* SQLITE_OMIT_VIRTUALTABLE */

 /*

 ** If the pBase expression originated in the ON or USING clause of

 ** a join, then transfer the appropriate markings over to derived.

 */

 static void transferJoinMarkings(Expr *pDerived, Expr *pBase){

   pDerived->flags |= pBase->flags & EP_FromJoin;

   pDerived->iRightJoinTable = pBase->iRightJoinTable;

 }

 #if !defined(SQLITE_OMIT_OR_OPTIMIZATION) && !defined(SQLITE_OMIT_SUBQUERY)

 /*

 ** Return TRUE if the given term of an OR clause can be converted

 ** into an IN clause.  The iCursor and iColumn define the left-hand

 ** side of the IN clause.

 **

 ** The context is that we have multiple OR-connected equality terms

 ** like this:

 **

 **           a=<expr1> OR  a=<expr2> OR b=<expr3>  OR ...

 **

 ** The pOrTerm input to this routine corresponds to a single term of

 ** this OR clause.  In order for the term to be a candidate for

 ** conversion to an IN operator, the following must be true:

 **

 **     *  The left-hand side of the term must be the column which

 **        is identified by iCursor and iColumn.

 **

 **     *  If the right-hand side is also a column, then the affinities

 **        of both right and left sides must be such that no type

 **        conversions are required on the right.  (Ticket #2249)

 **

 ** If both of these conditions are true, then return true.  Otherwise

 ** return false.

 */

 static int orTermIsOptCandidate(WhereTerm *pOrTerm, int iCursor, int iColumn){

   int affLeft, affRight;

   assert( pOrTerm->eOperator==WO_EQ );

   if( pOrTerm->leftCursor!=iCursor ){

     return 0;

   }

   if( pOrTerm->leftColumn!=iColumn ){

     return 0;

   }

   affRight = sqlite3ExprAffinity(pOrTerm->pExpr->pRight);

   if( affRight==0 ){

     return 1;

   }

   affLeft = sqlite3ExprAffinity(pOrTerm->pExpr->pLeft);

   if( affRight!=affLeft ){

     return 0;

   }

   return 1;

 }

 /*

 ** Return true if the given term of an OR clause can be ignored during

 ** a check to make sure all OR terms are candidates for optimization.

 ** In other words, return true if a call to the orTermIsOptCandidate()

 ** above returned false but it is not necessary to disqualify the

 ** optimization.

 **

 ** Suppose the original OR phrase was this:

 **

 **           a=4  OR  a=11  OR  a=b

 **

 ** During analysis, the third term gets flipped around and duplicate

 ** so that we are left with this:

 **

 **           a=4  OR  a=11  OR  a=b  OR  b=a

 **

 ** Since the last two terms are duplicates, only one of them

 ** has to qualify in order for the whole phrase to qualify.  When

 ** this routine is called, we know that pOrTerm did not qualify.

 ** This routine merely checks to see if pOrTerm has a duplicate that

 ** might qualify.  If there is a duplicate that has not yet been

 ** disqualified, then return true.  If there are no duplicates, or

 ** the duplicate has also been disqualified, return false.

 */

 static int orTermHasOkDuplicate(WhereClause *pOr, WhereTerm *pOrTerm){

   if( pOrTerm->flags & TERM_COPIED ){

     /* This is the original term.  The duplicate is to the left had

     ** has not yet been analyzed and thus has not yet been disqualified. */

     return 1;

   }

   if( (pOrTerm->flags & TERM_VIRTUAL)!=0

      && (pOr->a[pOrTerm->iParent].flags & TERM_OR_OK)!=0 ){

     /* This is a duplicate term.  The original qualified so this one

     ** does not have to. */

     return 1;

   }

   /* This is either a singleton term or else it is a duplicate for

   ** which the original did not qualify.  Either way we are done for. */

   return 0;

 }

 #endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */

 /*

 ** The input to this routine is an WhereTerm structure with only the

 ** "pExpr" field filled in.  The job of this routine is to analyze the

 ** subexpression and populate all the other fields of the WhereTerm

 ** structure.

 **

 ** If the expression is of the form "<expr> <op> X" it gets commuted

 ** to the standard form of "X <op> <expr>".  If the expression is of

 ** the form "X <op> Y" where both X and Y are columns, then the original

 ** expression is unchanged and a new virtual expression of the form

 ** "Y <op> X" is added to the WHERE clause and analyzed separately.

 */

 static void exprAnalyze(

   SrcList *pSrc,            /* the FROM clause */

   WhereClause *pWC,         /* the WHERE clause */

   int idxTerm               /* Index of the term to be analyzed */

 ){

   WhereTerm *pTerm;

   ExprMaskSet *pMaskSet;

   Expr *pExpr;

   Bitmask prereqLeft;

   Bitmask prereqAll;

   Bitmask extraRight = 0;

   int nPattern;

   int isComplete;

   int noCase;

   int op;

   Parse *pParse = pWC->pParse;

   sqlite3 *db = pParse->db;

   if( db->mallocFailed ){

     return;

   }

   pTerm = &pWC->a[idxTerm];

   pMaskSet = pWC->pMaskSet;

   pExpr = pTerm->pExpr;

   prereqLeft = exprTableUsage(pMaskSet, pExpr->pLeft);

   op = pExpr->op;

   if( op==TK_IN ){

     assert( pExpr->pRight==0 );

     pTerm->prereqRight = exprListTableUsage(pMaskSet, pExpr->pList)

                           | exprSelectTableUsage(pMaskSet, pExpr->pSelect);

   }else if( op==TK_ISNULL ){

     pTerm->prereqRight = 0;

   }else{

     pTerm->prereqRight = exprTableUsage(pMaskSet, pExpr->pRight);

   }

   prereqAll = exprTableUsage(pMaskSet, pExpr);

   if( ExprHasProperty(pExpr, EP_FromJoin) ){

     Bitmask x = getMask(pMaskSet, pExpr->iRightJoinTable);

     prereqAll |= x;

     extraRight = x-1;  /* ON clause terms may not be used with an index

                        ** on left table of a LEFT JOIN.  Ticket #3015 */

   }

   pTerm->prereqAll = prereqAll;

   pTerm->leftCursor = -1;

   pTerm->iParent = -1;

   pTerm->eOperator = 0;

   if( allowedOp(op) && (pTerm->prereqRight & prereqLeft)==0 ){

     Expr *pLeft = pExpr->pLeft;

     Expr *pRight = pExpr->pRight;

     if( pLeft->op==TK_COLUMN ){

       pTerm->leftCursor = pLeft->iTable;

       pTerm->leftColumn = pLeft->iColumn;

       pTerm->eOperator = operatorMask(op);

     }

     if( pRight && pRight->op==TK_COLUMN ){

       WhereTerm *pNew;

       Expr *pDup;

       if( pTerm->leftCursor>=0 ){

         int idxNew;

         pDup = sqlite3ExprDup(db, pExpr);

         if( db->mallocFailed ){

           sqlite3ExprDelete(db, pDup);

           return;

         }

         idxNew = whereClauseInsert(pWC, pDup, TERM_VIRTUAL|TERM_DYNAMIC);

         if( idxNew==0 ) return;

         pNew = &pWC->a[idxNew];

         pNew->iParent = idxTerm;

         pTerm = &pWC->a[idxTerm];

         pTerm->nChild = 1;

         pTerm->flags |= TERM_COPIED;

       }else{

         pDup = pExpr;

         pNew = pTerm;

       }

       exprCommute(pDup);

       pLeft = pDup->pLeft;

       pNew->leftCursor = pLeft->iTable;

       pNew->leftColumn = pLeft->iColumn;

       pNew->prereqRight = prereqLeft;

       pNew->prereqAll = prereqAll;

       pNew->eOperator = operatorMask(pDup->op);

     }

   }

 #ifndef SQLITE_OMIT_BETWEEN_OPTIMIZATION

   /* If a term is the BETWEEN operator, create two new virtual terms

   ** that define the range that the BETWEEN implements.

   */

   else if( pExpr->op==TK_BETWEEN ){

     ExprList *pList = pExpr->pList;

     int i;

     static const u8 ops[] = {TK_GE, TK_LE};

     assert( pList!=0 );

     assert( pList->nExpr==2 );

     for(i=0; i<2; i++){

       Expr *pNewExpr;

       int idxNew;

       pNewExpr = sqlite3Expr(db, ops[i], sqlite3ExprDup(db, pExpr->pLeft),

                              sqlite3ExprDup(db, pList->a[i].pExpr), 0);

       idxNew = whereClauseInsert(pWC, pNewExpr, TERM_VIRTUAL|TERM_DYNAMIC);

       exprAnalyze(pSrc, pWC, idxNew);

       pTerm = &pWC->a[idxTerm];

       pWC->a[idxNew].iParent = idxTerm;

     }

     pTerm->nChild = 2;

   }

 #endif /* SQLITE_OMIT_BETWEEN_OPTIMIZATION */

 #if !defined(SQLITE_OMIT_OR_OPTIMIZATION) && !defined(SQLITE_OMIT_SUBQUERY)

   /* Attempt to convert OR-connected terms into an IN operator so that

   ** they can make use of indices.  Example:

   **

   **      x = expr1  OR  expr2 = x  OR  x = expr3

   **

   ** is converted into

   **

   **      x IN (expr1,expr2,expr3)

   **

   ** This optimization must be omitted if OMIT_SUBQUERY is defined because

   ** the compiler for the the IN operator is part of sub-queries.

   */

   else if( pExpr->op==TK_OR ){

     int ok;

     int i, j;

     int iColumn, iCursor;

     WhereClause sOr;

     WhereTerm *pOrTerm;

     assert( (pTerm->flags & TERM_DYNAMIC)==0 );

     whereClauseInit(&sOr, pWC->pParse, pMaskSet);

     whereSplit(&sOr, pExpr, TK_OR);

     exprAnalyzeAll(pSrc, &sOr);

     assert( sOr.nTerm>=2 );

     j = 0;

     if( db->mallocFailed ) goto or_not_possible;

     do{

       assert( j<sOr.nTerm );

       iColumn = sOr.a[j].leftColumn;

       iCursor = sOr.a[j].leftCursor;

       ok = iCursor>=0;

       for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0 && ok; i--, pOrTerm++){

         if( pOrTerm->eOperator!=WO_EQ ){

           goto or_not_possible;

         }

         if( orTermIsOptCandidate(pOrTerm, iCursor, iColumn) ){

           pOrTerm->flags |= TERM_OR_OK;

         }else if( orTermHasOkDuplicate(&sOr, pOrTerm) ){

           pOrTerm->flags &= ~TERM_OR_OK;

         }else{

           ok = 0;

         }

       }

     }while( !ok && (sOr.a[j++].flags & TERM_COPIED)!=0 && j<2 );

     if( ok ){

       ExprList *pList = 0;

       Expr *pNew, *pDup;

       Expr *pLeft = 0;

       for(i=sOr.nTerm-1, pOrTerm=sOr.a; i>=0; i--, pOrTerm++){

         if( (pOrTerm->flags & TERM_OR_OK)==0 ) continue;

         pDup = sqlite3ExprDup(db, pOrTerm->pExpr->pRight);

         pList = sqlite3ExprListAppend(pWC->pParse, pList, pDup, 0);

         pLeft = pOrTerm->pExpr->pLeft;

       }

       assert( pLeft!=0 );

       pDup = sqlite3ExprDup(db, pLeft);

       pNew = sqlite3Expr(db, TK_IN, pDup, 0, 0);

       if( pNew ){

         int idxNew;

         transferJoinMarkings(pNew, pExpr);

         pNew->pList = pList;

         idxNew = whereClauseInsert(pWC, pNew, TERM_VIRTUAL|TERM_DYNAMIC);

         exprAnalyze(pSrc, pWC, idxNew);

         pTerm = &pWC->a[idxTerm];

         pWC->a[idxNew].iParent = idxTerm;

         pTerm->nChild = 1;

       }else{

         sqlite3ExprListDelete(db, pList);

       }

     }

 or_not_possible:

     whereClauseClear(&sOr);

   }

 #endif /* SQLITE_OMIT_OR_OPTIMIZATION */

 #ifndef SQLITE_OMIT_LIKE_OPTIMIZATION

   /* Add constraints to reduce the search space on a LIKE or GLOB

   ** operator.

   **

   ** A like pattern of the form "x LIKE 'abc%'" is changed into constraints

   **

   **          x>='abc' AND x<'abd' AND x LIKE 'abc%'

   **

   ** The last character of the prefix "abc" is incremented to form the

   ** termination condition "abd".

   */

   if( isLikeOrGlob(db, pExpr, &nPattern, &isComplete, &noCase) ){

     Expr *pLeft, *pRight;

     Expr *pStr1, *pStr2;

     Expr *pNewExpr1, *pNewExpr2;

     int idxNew1, idxNew2;

     pLeft = pExpr->pList->a[1].pExpr;

     pRight = pExpr->pList->a[0].pExpr;

     pStr1 = sqlite3PExpr(pParse, TK_STRING, 0, 0, 0);

     if( pStr1 ){

       sqlite3TokenCopy(db, &pStr1->token, &pRight->token);

       pStr1->token.n = nPattern;

       pStr1->flags = EP_Dequoted;

     }

     pStr2 = sqlite3ExprDup(db, pStr1);

     if( !db->mallocFailed ){

       u8 c, *pC;

       assert( pStr2->token.dyn );

       pC = (u8*)&pStr2->token.z[nPattern-1];

       c = *pC;

       if( noCase ){

         if( c=='@' ) isComplete = 0;

         c = sqlite3UpperToLower[c];

       }

       *pC = c + 1;

     }

     pNewExpr1 = sqlite3PExpr(pParse, TK_GE, sqlite3ExprDup(db,pLeft), pStr1, 0);

     idxNew1 = whereClauseInsert(pWC, pNewExpr1, TERM_VIRTUAL|TERM_DYNAMIC);

     exprAnalyze(pSrc, pWC, idxNew1);

     pNewExpr2 = sqlite3PExpr(pParse, TK_LT, sqlite3ExprDup(db,pLeft), pStr2, 0);

     idxNew2 = whereClauseInsert(pWC, pNewExpr2, TERM_VIRTUAL|TERM_DYNAMIC);

     exprAnalyze(pSrc, pWC, idxNew2);

     pTerm = &pWC->a[idxTerm];

     if( isComplete ){

       pWC->a[idxNew1].iParent = idxTerm;

       pWC->a[idxNew2].iParent = idxTerm;

       pTerm->nChild = 2;

     }

   }

 #endif /* SQLITE_OMIT_LIKE_OPTIMIZATION */

 #ifndef SQLITE_OMIT_VIRTUALTABLE

   /* Add a WO_MATCH auxiliary term to the constraint set if the

   ** current expression is of the form:  column MATCH expr.

   ** This information is used by the xBestIndex methods of

   ** virtual tables.  The native query optimizer does not attempt

   ** to do anything with MATCH functions.

   */

   if( isMatchOfColumn(pExpr) ){

     int idxNew;

     Expr *pRight, *pLeft;

     WhereTerm *pNewTerm;

     Bitmask prereqColumn, prereqExpr;

     pRight = pExpr->pList->a[0].pExpr;

     pLeft = pExpr->pList->a[1].pExpr;

     prereqExpr = exprTableUsage(pMaskSet, pRight);

     prereqColumn = exprTableUsage(pMaskSet, pLeft);

     if( (prereqExpr & prereqColumn)==0 ){

       Expr *pNewExpr;

       pNewExpr = sqlite3Expr(db, TK_MATCH, 0, sqlite3ExprDup(db, pRight), 0);

       idxNew = whereClauseInsert(pWC, pNewExpr, TERM_VIRTUAL|TERM_DYNAMIC);

       pNewTerm = &pWC->a[idxNew];

       pNewTerm->prereqRight = prereqExpr;

       pNewTerm->leftCursor = pLeft->iTable;

       pNewTerm->leftColumn = pLeft->iColumn;

       pNewTerm->eOperator = WO_MATCH;

       pNewTerm->iParent = idxTerm;

       pTerm = &pWC->a[idxTerm];

       pTerm->nChild = 1;

       pTerm->flags |= TERM_COPIED;

       pNewTerm->prereqAll = pTerm->prereqAll;

     }

   }

 #endif /* SQLITE_OMIT_VIRTUALTABLE */

   /* Prevent ON clause terms of a LEFT JOIN from being used to drive

   ** an index for tables to the left of the join.

   */

   pTerm->prereqRight |= extraRight;

 }

 /*

 ** Return TRUE if any of the expressions in pList->a[iFirst...] contain

 ** a reference to any table other than the iBase table.

 */

 static int referencesOtherTables(

   ExprList *pList,          /* Search expressions in ths list */

   ExprMaskSet *pMaskSet,    /* Mapping from tables to bitmaps */

   int iFirst,               /* Be searching with the iFirst-th expression */

   int iBase                 /* Ignore references to this table */

 ){

   Bitmask allowed = ~getMask(pMaskSet, iBase);

   while( iFirst<pList->nExpr ){

     if( (exprTableUsage(pMaskSet, pList->a[iFirst++].pExpr)&allowed)!=0 ){

       return 1;

     }

   }

   return 0;

 }

 /*

 ** This routine decides if pIdx can be used to satisfy the ORDER BY

 ** clause.  If it can, it returns 1.  If pIdx cannot satisfy the

 ** ORDER BY clause, this routine returns 0.

 **

 ** pOrderBy is an ORDER BY clause from a SELECT statement.  pTab is the

 ** left-most table in the FROM clause of that same SELECT statement and

 ** the table has a cursor number of "base".  pIdx is an index on pTab.

 **

 ** nEqCol is the number of columns of pIdx that are used as equality

 ** constraints.  Any of these columns may be missing from the ORDER BY

 ** clause and the match can still be a success.

 **

 ** All terms of the ORDER BY that match against the index must be either

 ** ASC or DESC.  (Terms of the ORDER BY clause past the end of a UNIQUE

 ** index do not need to satisfy this constraint.)  The *pbRev value is

 ** set to 1 if the ORDER BY clause is all DESC and it is set to 0 if

 ** the ORDER BY clause is all ASC.

 */

 static int isSortingIndex(

   Parse *pParse,          /* Parsing context */

   ExprMaskSet *pMaskSet,  /* Mapping from table indices to bitmaps */

   Index *pIdx,            /* The index we are testing */

   int base,               /* Cursor number for the table to be sorted */

   ExprList *pOrderBy,     /* The ORDER BY clause */

   int nEqCol,             /* Number of index columns with == constraints */

   int *pbRev              /* Set to 1 if ORDER BY is DESC */

 ){

   int i, j;                       /* Loop counters */

   int sortOrder = 0;              /* XOR of index and ORDER BY sort direction */

   int nTerm;                      /* Number of ORDER BY terms */

   struct ExprList_item *pTerm;    /* A term of the ORDER BY clause */

   sqlite3 *db = pParse->db;

   assert( pOrderBy!=0 );

   nTerm = pOrderBy->nExpr;

   assert( nTerm>0 );

   /* Match terms of the ORDER BY clause against columns of

   ** the index.

   **

   ** Note that indices have pIdx->nColumn regular columns plus

   ** one additional column containing the rowid.  The rowid column

   ** of the index is also allowed to match against the ORDER BY

   ** clause.

   */

   for(i=j=0, pTerm=pOrderBy->a; j<nTerm && i<=pIdx->nColumn; i++){

     Expr *pExpr;       /* The expression of the ORDER BY pTerm */

     CollSeq *pColl;    /* The collating sequence of pExpr */

     int termSortOrder; /* Sort order for this term */

     int iColumn;       /* The i-th column of the index.  -1 for rowid */

     int iSortOrder;    /* 1 for DESC, 0 for ASC on the i-th index term */

     const char *zColl; /* Name of the collating sequence for i-th index term */

     pExpr = pTerm->pExpr;

     if( pExpr->op!=TK_COLUMN || pExpr->iTable!=base ){

       /* Can not use an index sort on anything that is not a column in the

       ** left-most table of the FROM clause */

       break;

     }

     pColl = sqlite3ExprCollSeq(pParse, pExpr);

     if( !pColl ){

       pColl = db->pDfltColl;

     }

     if( i<pIdx->nColumn ){

       iColumn = pIdx->aiColumn[i];

       if( iColumn==pIdx->pTable->iPKey ){

         iColumn = -1;

       }

       iSortOrder = pIdx->aSortOrder[i];

       zColl = pIdx->azColl[i];

     }else{

       iColumn = -1;

       iSortOrder = 0;

       zColl = pColl->zName;

     }

     if( pExpr->iColumn!=iColumn || sqlite3StrICmp(pColl->zName, zColl) ){

       /* Term j of the ORDER BY clause does not match column i of the index */

       if( i<nEqCol ){

         /* If an index column that is constrained by == fails to match an

         ** ORDER BY term, that is OK.  Just ignore that column of the index

         */

         continue;

       }else if( i==pIdx->nColumn ){

         /* Index column i is the rowid.  All other terms match. */

         break;

       }else{

         /* If an index column fails to match and is not constrained by ==

         ** then the index cannot satisfy the ORDER BY constraint.

         */

         return 0;

       }

     }

     assert( pIdx->aSortOrder!=0 );

     assert( pTerm->sortOrder==0 || pTerm->sortOrder==1 );

     assert( iSortOrder==0 || iSortOrder==1 );

     termSortOrder = iSortOrder ^ pTerm->sortOrder;

     if( i>nEqCol ){

       if( termSortOrder!=sortOrder ){

         /* Indices can only be used if all ORDER BY terms past the

         ** equality constraints are all either DESC or ASC. */

         return 0;

       }

     }else{

       sortOrder = termSortOrder;

     }

     j++;

     pTerm++;

     if( iColumn<0 && !referencesOtherTables(pOrderBy, pMaskSet, j, base) ){

       /* If the indexed column is the primary key and everything matches

       ** so far and none of the ORDER BY terms to the right reference other

       ** tables in the join, then we are assured that the index can be used 

       ** to sort because the primary key is unique and so none of the other

       ** columns will make any difference

       */

       j = nTerm;

     }

   }

   *pbRev = sortOrder!=0;

   if( j>=nTerm ){

     /* All terms of the ORDER BY clause are covered by this index so

     ** this index can be used for sorting. */

     return 1;

   }

   if( pIdx->onError!=OE_None && i==pIdx->nColumn

       && !referencesOtherTables(pOrderBy, pMaskSet, j, base) ){

     /* All terms of this index match some prefix of the ORDER BY clause

     ** and the index is UNIQUE and no terms on the tail of the ORDER BY

     ** clause reference other tables in a join.  If this is all true then

     ** the order by clause is superfluous. */

     return 1;

   }

   return 0;

 }

 /*

 ** Check table to see if the ORDER BY clause in pOrderBy can be satisfied

 ** by sorting in order of ROWID.  Return true if so and set *pbRev to be

 ** true for reverse ROWID and false for forward ROWID order.

 */

 static int sortableByRowid(

   int base,               /* Cursor number for table to be sorted */

   ExprList *pOrderBy,     /* The ORDER BY clause */

   ExprMaskSet *pMaskSet,  /* Mapping from tables to bitmaps */

   int *pbRev              /* Set to 1 if ORDER BY is DESC */

 ){

   Expr *p;

   assert( pOrderBy!=0 );

   assert( pOrderBy->nExpr>0 );

   p = pOrderBy->a[0].pExpr;

   if( p->op==TK_COLUMN && p->iTable==base && p->iColumn==-1

     && !referencesOtherTables(pOrderBy, pMaskSet, 1, base) ){

     *pbRev = pOrderBy->a[0].sortOrder;

     return 1;

   }

   return 0;

 }

 /*

 ** Prepare a crude estimate of the logarithm of the input value.

 ** The results need not be exact.  This is only used for estimating

 ** the total cost of performing operations with O(logN) or O(NlogN)

 ** complexity.  Because N is just a guess, it is no great tragedy if

 ** logN is a little off.

 */

 static double estLog(double N){

   double logN = 1;

   double x = 10;

   while( N>x ){

     logN += 1;

     x *= 10;

   }

   return logN;

 }

 /*

 ** Two routines for printing the content of an sqlite3_index_info

 ** structure.  Used for testing and debugging only.  If neither

 ** SQLITE_TEST or SQLITE_DEBUG are defined, then these routines

 ** are no-ops.

 */

 #if !defined(SQLITE_OMIT_VIRTUALTABLE) && defined(SQLITE_DEBUG)

 static void TRACE_IDX_INPUTS(sqlite3_index_info *p){

   int i;

   if( !sqlite3WhereTrace ) return;

   for(i=0; i<p->nConstraint; i++){

     sqlite3DebugPrintf("  constraint[%d]: col=%d termid=%d op=%d usabled=%d\n",

        i,

        p->aConstraint[i].iColumn,

        p->aConstraint[i].iTermOffset,

        p->aConstraint[i].op,

        p->aConstraint[i].usable);

   }

   for(i=0; i<p->nOrderBy; i++){

     sqlite3DebugPrintf("  orderby[%d]: col=%d desc=%d\n",

        i,

        p->aOrderBy[i].iColumn,

        p->aOrderBy[i].desc);

   }

 }

 static void TRACE_IDX_OUTPUTS(sqlite3_index_info *p){

   int i;

   if( !sqlite3WhereTrace ) return;

   for(i=0; i<p->nConstraint; i++){

     sqlite3DebugPrintf("  usage[%d]: argvIdx=%d omit=%d\n",

        i,

        p->aConstraintUsage[i].argvIndex,

        p->aConstraintUsage[i].omit);

   }

   sqlite3DebugPrintf("  idxNum=%d\n", p->idxNum);

   sqlite3DebugPrintf("  idxStr=%s\n", p->idxStr);

   sqlite3DebugPrintf("  orderByConsumed=%d\n", p->orderByConsumed);

   sqlite3DebugPrintf("  estimatedCost=%g\n", p->estimatedCost);

 }

 #else

 #define TRACE_IDX_INPUTS(A)

 #define TRACE_IDX_OUTPUTS(A)

 #endif

 #ifndef SQLITE_OMIT_VIRTUALTABLE

 /*

 ** Compute the best index for a virtual table.

 **

 ** The best index is computed by the xBestIndex method of the virtual

 ** table module.  This routine is really just a wrapper that sets up

 ** the sqlite3_index_info structure that is used to communicate with

 ** xBestIndex.

 **

 ** In a join, this routine might be called multiple times for the

 ** same virtual table.  The sqlite3_index_info structure is created

 ** and initialized on the first invocation and reused on all subsequent

 ** invocations.  The sqlite3_index_info structure is also used when

 ** code is generated to access the virtual table.  The whereInfoDelete() 

 ** routine takes care of freeing the sqlite3_index_info structure after

 ** everybody has finished with it.

 */

 static double bestVirtualIndex(

   Parse *pParse,                 /* The parsing context */

   WhereClause *pWC,              /* The WHERE clause */

   struct SrcList_item *pSrc,     /* The FROM clause term to search */

   Bitmask notReady,              /* Mask of cursors that are not available */

   ExprList *pOrderBy,            /* The order by clause */

   int orderByUsable,             /* True if we can potential sort */

   sqlite3_index_info **ppIdxInfo /* Index information passed to xBestIndex */

 ){

   Table *pTab = pSrc->pTab;

   sqlite3_vtab *pVtab = pTab->pVtab;

   sqlite3_index_info *pIdxInfo;

   struct sqlite3_index_constraint *pIdxCons;

   struct sqlite3_index_orderby *pIdxOrderBy;

   struct sqlite3_index_constraint_usage *pUsage;

   WhereTerm *pTerm;

   int i, j;

   int nOrderBy;

   int rc;

   /* If the sqlite3_index_info structure has not been previously

   ** allocated and initialized for this virtual table, then allocate

   ** and initialize it now

   */

   pIdxInfo = *ppIdxInfo;

   if( pIdxInfo==0 ){

     WhereTerm *pTerm;

     int nTerm;

     WHERETRACE(("Recomputing index info for %s...\n", pTab->zName));

     /* Count the number of possible WHERE clause constraints referring

     ** to this virtual table */

     for(i=nTerm=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){

       if( pTerm->leftCursor != pSrc->iCursor ) continue;

       if( (pTerm->eOperator&(pTerm->eOperator-1))==0 );

       testcase( pTerm->eOperator==WO_IN );

       testcase( pTerm->eOperator==WO_ISNULL );

       if( pTerm->eOperator & (WO_IN|WO_ISNULL) ) continue;

       nTerm++;

     }

     /* If the ORDER BY clause contains only columns in the current 

     ** virtual table then allocate space for the aOrderBy part of

     ** the sqlite3_index_info structure.

     */

     nOrderBy = 0;

     if( pOrderBy ){

       for(i=0; i<pOrderBy->nExpr; i++){

         Expr *pExpr = pOrderBy->a[i].pExpr;

         if( pExpr->op!=TK_COLUMN || pExpr->iTable!=pSrc->iCursor ) break;

       }

       if( i==pOrderBy->nExpr ){

         nOrderBy = pOrderBy->nExpr;

       }

     }

     /* Allocate the sqlite3_index_info structure

     */

     pIdxInfo = sqlite3DbMallocZero(pParse->db, sizeof(*pIdxInfo)

                              + (sizeof(*pIdxCons) + sizeof(*pUsage))*nTerm

                              + sizeof(*pIdxOrderBy)*nOrderBy );

     if( pIdxInfo==0 ){

       sqlite3ErrorMsg(pParse, "out of memory");

       return 0.0;

     }

     *ppIdxInfo = pIdxInfo;

     /* Initialize the structure.  The sqlite3_index_info structure contains

     ** many fields that are declared "const" to prevent xBestIndex from

     ** changing them.  We have to do some funky casting in order to

     ** initialize those fields.

     */

     pIdxCons = (struct sqlite3_index_constraint*)&pIdxInfo[1];

     pIdxOrderBy = (struct sqlite3_index_orderby*)&pIdxCons[nTerm];

     pUsage = (struct sqlite3_index_constraint_usage*)&pIdxOrderBy[nOrderBy];

     *(int*)&pIdxInfo->nConstraint = nTerm;

     *(int*)&pIdxInfo->nOrderBy = nOrderBy;

     *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint = pIdxCons;

     *(struct sqlite3_index_orderby**)&pIdxInfo->aOrderBy = pIdxOrderBy;

     *(struct sqlite3_index_constraint_usage**)&pIdxInfo->aConstraintUsage =

                                                                      pUsage;

     for(i=j=0, pTerm=pWC->a; i<pWC->nTerm; i++, pTerm++){

       if( pTerm->leftCursor != pSrc->iCursor ) continue;

       if( (pTerm->eOperator&(pTerm->eOperator-1))==0 );

       testcase( pTerm->eOperator==WO_IN );

       testcase( pTerm->eOperator==WO_ISNULL );

       if( pTerm->eOperator & (WO_IN|WO_ISNULL) ) continue;

       pIdxCons[j].iColumn = pTerm->leftColumn;

       pIdxCons[j].iTermOffset = i;

       pIdxCons[j].op = pTerm->eOperator;

       /* The direct assignment in the previous line is possible only because

       ** the WO_ and SQLITE_INDEX_CONSTRAINT_ codes are identical.  The

       ** following asserts verify this fact. */

       assert( WO_EQ==SQLITE_INDEX_CONSTRAINT_EQ );

       assert( WO_LT==SQLITE_INDEX_CONSTRAINT_LT );

       assert( WO_LE==SQLITE_INDEX_CONSTRAINT_LE );

       assert( WO_GT==SQLITE_INDEX_CONSTRAINT_GT );

       assert( WO_GE==SQLITE_INDEX_CONSTRAINT_GE );

       assert( WO_MATCH==SQLITE_INDEX_CONSTRAINT_MATCH );

       assert( pTerm->eOperator & (WO_EQ|WO_LT|WO_LE|WO_GT|WO_GE|WO_MATCH) );

       j++;

     }

     for(i=0; i<nOrderBy; i++){

       Expr *pExpr = pOrderBy->a[i].pExpr;

       pIdxOrderBy[i].iColumn = pExpr->iColumn;

       pIdxOrderBy[i].desc = pOrderBy->a[i].sortOrder;

     }

   }

   /* At this point, the sqlite3_index_info structure that pIdxInfo points

   ** to will have been initialized, either during the current invocation or

   ** during some prior invocation.  Now we just have to customize the

   ** details of pIdxInfo for the current invocation and pass it to

   ** xBestIndex.

   */

   /* The module name must be defined. Also, by this point there must

   ** be a pointer to an sqlite3_vtab structure. Otherwise

   ** sqlite3ViewGetColumnNames() would have picked up the error. 

   */

   assert( pTab->azModuleArg && pTab->azModuleArg[0] );

   assert( pVtab );

 #if 0

   if( pTab->pVtab==0 ){

     sqlite3ErrorMsg(pParse, "undefined module %s for table %s",

         pTab->azModuleArg[0], pTab->zName);

     return 0.0;

   }

 #endif

   /* Set the aConstraint[].usable fields and initialize all 

   ** output variables to zero.

   **

   ** aConstraint[].usable is true for constraints where the right-hand

   ** side contains only references to tables to the left of the current

   ** table.  In other words, if the constraint is of the form:

   **

   **           column = expr

   **

   ** and we are evaluating a join, then the constraint on column is 

   ** only valid if all tables referenced in expr occur to the left

   ** of the table containing column.

   **

   ** The aConstraints[] array contains entries for all constraints

   ** on the current table.  That way we only have to compute it once

   ** even though we might try to pick the best index multiple times.

   ** For each attempt at picking an index, the order of tables in the

   ** join might be different so we have to recompute the usable flag

   ** each time.

   */

   pIdxCons = *(struct sqlite3_index_constraint**)&pIdxInfo->aConstraint;

   pUsage = pIdxInfo->aConstraintUsage;

   for(i=0; i<pIdxInfo->nConstraint; i++, pIdxCons++){

     j = pIdxCons->iTermOffset;

     pTerm = &pWC->a[j];

     pIdxCons->usable =  (pTerm->prereqRight & notReady)==0;

   }

   memset(pUsage, 0, sizeof(pUsage[0])*pIdxInfo->nConstraint);

   if( pIdxInfo->needToFreeIdxStr ){

     sqlite3_free(pIdxInfo->idxStr);

   }

   pIdxInfo->idxStr = 0;

   pIdxInfo->idxNum = 0;

   pIdxInfo->needToFreeIdxStr = 0;

   pIdxInfo->orderByConsumed = 0;

   pIdxInfo->estimatedCost = SQLITE_BIG_DBL / 2.0;

   nOrderBy = pIdxInfo->nOrderBy;

   if( pIdxInfo->nOrderBy && !orderByUsable ){

     *(int*)&pIdxInfo->nOrderBy = 0;

   }

   (void)sqlite3SafetyOff(pParse->db);

   WHERETRACE(("xBestIndex for %s\n", pTab->zName));

   TRACE_IDX_INPUTS(pIdxInfo);

   rc = pVtab->pModule->xBestIndex(pVtab, pIdxInfo);

   TRACE_IDX_OUTPUTS(pIdxInfo);

   (void)sqlite3SafetyOn(pParse->db);

   if( rc!=SQLITE_OK ){

     if( rc==SQLITE_NOMEM ){

       pParse->db->mallocFailed = 1;

     }else if( !pVtab->zErrMsg ){

       sqlite3ErrorMsg(pParse, "%s", sqlite3ErrStr(rc));

     }else{

       sqlite3ErrorMsg(pParse, "%s", pVtab->zErrMsg);

     }

   }

   sqlite3DbFree(pParse->db, pVtab->zErrMsg);

   pVtab->zErrMsg = 0;

   for(i=0; i<pIdxInfo->nConstraint; i++){

     if( !pIdxInfo->aConstraint[i].usable && pUsage[i].argvIndex>0 ){

       sqlite3ErrorMsg(pParse, 

           "table %s: xBestIndex returned an invalid plan", pTab->zName);

       return 0.0;

     }

   }

   *(int*)&pIdxInfo->nOrderBy = nOrderBy;

   return pIdxInfo->estimatedCost;

 }

 #endif /* SQLITE_OMIT_VIRTUALTABLE */

 /*

 ** Find the best index for accessing a particular table.  Return a pointer

 ** to the index, flags that describe how the index should be used, the

 ** number of equality constraints, and the "cost" for this index.

 **

 ** The lowest cost index wins.  The cost is an estimate of the amount of

 ** CPU and disk I/O need to process the request using the selected index.

 ** Factors that influence cost include:

 **

 **    *  The estimated number of rows that will be retrieved.  (The

 **       fewer the better.)

 **

 **    *  Whether or not sorting must occur.

 **

 **    *  Whether or not there must be separate lookups in the

 **       index and in the main table.

 **

 */

 static double bestIndex(

   Parse *pParse,              /* The parsing context */

   WhereClause *pWC,           /* The WHERE clause */

   struct SrcList_item *pSrc,  /* The FROM clause term to search */

   Bitmask notReady,           /* Mask of cursors that are not available */

   ExprList *pOrderBy,         /* The order by clause */

   Index **ppIndex,            /* Make *ppIndex point to the best index */

   int *pFlags,                /* Put flags describing this choice in *pFlags */

   int *pnEq                   /* Put the number of == or IN constraints here */

 ){

   WhereTerm *pTerm;

   Index *bestIdx = 0;         /* Index that gives the lowest cost */

   double lowestCost;          /* The cost of using bestIdx */

   int bestFlags = 0;          /* Flags associated with bestIdx */

   int bestNEq = 0;            /* Best value for nEq */

   int iCur = pSrc->iCursor;   /* The cursor of the table to be accessed */

   Index *pProbe;              /* An index we are evaluating */

   int rev;                    /* True to scan in reverse order */

   int flags;                  /* Flags associated with pProbe */

   int nEq;                    /* Number of == or IN constraints */

   int eqTermMask;             /* Mask of valid equality operators */

   double cost;                /* Cost of using pProbe */

   WHERETRACE(("bestIndex: tbl=%s notReady=%llx\n", pSrc->pTab->zName, notReady));

   lowestCost = SQLITE_BIG_DBL;

   pProbe = pSrc->pTab->pIndex;

   /* If the table has no indices and there are no terms in the where

   ** clause that refer to the ROWID, then we will never be able to do

   ** anything other than a full table scan on this table.  We might as

   ** well put it first in the join order.  That way, perhaps it can be

   ** referenced by other tables in the join.

   */

   if( pProbe==0 &&

      findTerm(pWC, iCur, -1, 0, WO_EQ|WO_IN|WO_LT|WO_LE|WO_GT|WO_GE,0)==0 &&

      (pOrderBy==0 || !sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev)) ){

     *pFlags = 0;

     *ppIndex = 0;

     *pnEq = 0;

     return 0.0;

   }

   /* Check for a rowid=EXPR or rowid IN (...) constraints

   */

   pTerm = findTerm(pWC, iCur, -1, notReady, WO_EQ|WO_IN, 0);

   if( pTerm ){

     Expr *pExpr;

     *ppIndex = 0;

     bestFlags = WHERE_ROWID_EQ;

     if( pTerm->eOperator & WO_EQ ){

       /* Rowid== is always the best pick.  Look no further.  Because only

       ** a single row is generated, output is always in sorted order */

       *pFlags = WHERE_ROWID_EQ | WHERE_UNIQUE;

       *pnEq = 1;

       WHERETRACE(("... best is rowid\n"));

       return 0.0;

     }else if( (pExpr = pTerm->pExpr)->pList!=0 ){

       /* Rowid IN (LIST): cost is NlogN where N is the number of list

       ** elements.  */

       lowestCost = pExpr->pList->nExpr;

       lowestCost *= estLog(lowestCost);

     }else{

       /* Rowid IN (SELECT): cost is NlogN where N is the number of rows

       ** in the result of the inner select.  We have no way to estimate

       ** that value so make a wild guess. */

       lowestCost = 200;

     }

     WHERETRACE(("... rowid IN cost: %.9g\n", lowestCost));

   }

   /* Estimate the cost of a table scan.  If we do not know how many

   ** entries are in the table, use 1 million as a guess.

   */

   cost = pProbe ? pProbe->aiRowEst[0] : 1000000;

   WHERETRACE(("... table scan base cost: %.9g\n", cost));

   flags = WHERE_ROWID_RANGE;

   /* Check for constraints on a range of rowids in a table scan.

   */

   pTerm = findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE|WO_GT|WO_GE, 0);

   if( pTerm ){

     if( findTerm(pWC, iCur, -1, notReady, WO_LT|WO_LE, 0) ){

       flags |= WHERE_TOP_LIMIT;

       cost /= 3;  /* Guess that rowid<EXPR eliminates two-thirds or rows */

     }

     if( findTerm(pWC, iCur, -1, notReady, WO_GT|WO_GE, 0) ){

       flags |= WHERE_BTM_LIMIT;

       cost /= 3;  /* Guess that rowid>EXPR eliminates two-thirds of rows */

     }

     WHERETRACE(("... rowid range reduces cost to %.9g\n", cost));

   }else{

     flags = 0;

   }

   /* If the table scan does not satisfy the ORDER BY clause, increase

   ** the cost by NlogN to cover the expense of sorting. */

   if( pOrderBy ){

     if( sortableByRowid(iCur, pOrderBy, pWC->pMaskSet, &rev) ){

       flags |= WHERE_ORDERBY|WHERE_ROWID_RANGE;

       if( rev ){

         flags |= WHERE_REVERSE;

       }

     }else{

       cost += cost*estLog(cost);

       WHERETRACE(("... sorting increases cost to %.9g\n", cost));

     }

   }

   if( cost<lowestCost ){

     lowestCost = cost;

     bestFlags = flags;

   }

   /* If the pSrc table is the right table of a LEFT JOIN then we may not

   ** use an index to satisfy IS NULL constraints on that table.  This is

   ** because columns might end up being NULL if the table does not match -

   ** a circumstance which the index cannot help us discover.  Ticket #2177.

   */

   if( (pSrc->jointype & JT_LEFT)!=0 ){

     eqTermMask = WO_EQ|WO_IN;

   }else{

     eqTermMask = WO_EQ|WO_IN|WO_ISNULL;

   }

   /* Look at each index.

   */

   for(; pProbe; pProbe=pProbe->pNext){

     int i;                       /* Loop counter */

     double inMultiplier = 1;

     WHERETRACE(("... index %s:\n", pProbe->zName));

     /* Count the number of columns in the index that are satisfied

     ** by x=EXPR constraints or x IN (...) constraints.

     */

     flags = 0;

     for(i=0; i<pProbe->nColumn; i++){

       int j = pProbe->aiColumn[i];

       pTerm = findTerm(pWC, iCur, j, notReady, eqTermMask, pProbe);

       if( pTerm==0 ) break;

       flags |= WHERE_COLUMN_EQ;

       if( pTerm->eOperator & WO_IN ){

         Expr *pExpr = pTerm->pExpr;

         flags |= WHERE_COLUMN_IN;

         if( pExpr->pSelect!=0 ){

           inMultiplier *= 25;

         }else if( ALWAYS(pExpr->pList) ){

           inMultiplier *= pExpr->pList->nExpr + 1;

         }

       }

     }

     cost = pProbe->aiRowEst[i] * inMultiplier * estLog(inMultiplier);

     nEq = i;

     if( pProbe->onError!=OE_None && (flags & WHERE_COLUMN_IN)==0

          && nEq==pProbe->nColumn ){

       flags |= WHERE_UNIQUE;

     }

     WHERETRACE(("...... nEq=%d inMult=%.9g cost=%.9g\n",nEq,inMultiplier,cost));

     /* Look for range constraints

     */

     if( nEq<pProbe->nColumn ){

       int j = pProbe->aiColumn[nEq];

       pTerm = findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE|WO_GT|WO_GE, pProbe);

       if( pTerm ){

         flags |= WHERE_COLUMN_RANGE;

         if( findTerm(pWC, iCur, j, notReady, WO_LT|WO_LE, pProbe) ){

           flags |= WHERE_TOP_LIMIT;

           cost /= 3;

         }

         if( findTerm(pWC, iCur, j, notReady, WO_GT|WO_GE, pProbe) ){

           flags |= WHERE_BTM_LIMIT;

           cost /= 3;

         }

         WHERETRACE(("...... range reduces cost to %.9g\n", cost));

       }

     }

     /* Add the additional cost of sorting if that is a factor.

     */

     if( pOrderBy ){

       if( (flags & WHERE_COLUMN_IN)==0 &&

            isSortingIndex(pParse,pWC->pMaskSet,pProbe,iCur,pOrderBy,nEq,&rev) ){

         if( flags==0 ){

           flags = WHERE_COLUMN_RANGE;

         }

         flags |= WHERE_ORDERBY;

         if( rev ){

           flags |= WHERE_REVERSE;

         }

       }else{

         cost += cost*estLog(cost);

         WHERETRACE(("...... orderby increases cost to %.9g\n", cost));

       }

     }

     /* Check to see if we can get away with using just the index without

     ** ever reading the table.  If that is the case, then halve the

     ** cost of this index.

     */

     if( flags && pSrc->colUsed < (((Bitmask)1)<<(BMS-1)) ){

       Bitmask m = pSrc->colUsed;

       int j;

       for(j=0; j<pProbe->nColumn; j++){

         int x = pProbe->aiColumn[j];

         if( x<BMS-1 ){

           m &= ~(((Bitmask)1)<<x);

         }

       }

       if( m==0 ){

         flags |= WHERE_IDX_ONLY;

         cost /= 2;

         WHERETRACE(("...... idx-only reduces cost to %.9g\n", cost));

       }

     }

     /* If this index has achieved the lowest cost so far, then use it.

     */

     if( flags && cost < lowestCost ){

       bestIdx = pProbe;

       lowestCost = cost;

       bestFlags = flags;

       bestNEq = nEq;

     }

   }

   /* Report the best result

   */

   *ppIndex = bestIdx;

   WHERETRACE(("best index is %s, cost=%.9g, flags=%x, nEq=%d\n",

         bestIdx ? bestIdx->zName : "(none)", lowestCost, bestFlags, bestNEq));

   *pFlags = bestFlags | eqTermMask;

   *pnEq = bestNEq;

   return lowestCost;

 }

 /*

 ** Disable a term in the WHERE clause.  Except, do not disable the term

 ** if it controls a LEFT OUTER JOIN and it did not originate in the ON

 ** or USING clause of that join.

 **

 ** Consider the term t2.z='ok' in the following queries:

 **

 **   (1)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x WHERE t2.z='ok'

 **   (2)  SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.x AND t2.z='ok'

 **   (3)  SELECT * FROM t1, t2 WHERE t1.a=t2.x AND t2.z='ok'

 **

 ** The t2.z='ok' is disabled in the in (2) because it originates

 ** in the ON clause.  The term is disabled in (3) because it is not part

 ** of a LEFT OUTER JOIN.  In (1), the term is not disabled.

 **

 ** Disabling a term causes that term to not be tested in the inner loop

 ** of the join.  Disabling is an optimization.  When terms are satisfied

 ** by indices, we disable them to prevent redundant tests in the inner

 ** loop.  We would get the correct results if nothing were ever disabled,

 ** but joins might run a little slower.  The trick is to disable as much

 ** as we can without disabling too much.  If we disabled in (1), we'd get

 ** the wrong answer.  See ticket #813.

 */

 static void disableTerm(WhereLevel *pLevel, WhereTerm *pTerm){

   if( pTerm

       && ALWAYS((pTerm->flags & TERM_CODED)==0)

       && (pLevel->iLeftJoin==0 || ExprHasProperty(pTerm->pExpr, EP_FromJoin))

   ){

     pTerm->flags |= TERM_CODED;

     if( pTerm->iParent>=0 ){

       WhereTerm *pOther = &pTerm->pWC->a[pTerm->iParent];

       if( (--pOther->nChild)==0 ){

         disableTerm(pLevel, pOther);

       }

     }

   }

 }

 /*

 ** Apply the affinities associated with the first n columns of index

 ** pIdx to the values in the n registers starting at base.

 */

 static void codeApplyAffinity(Parse *pParse, int base, int n, Index *pIdx){

   if( n>0 ){

     Vdbe *v = pParse->pVdbe;

     assert( v!=0 );

     sqlite3VdbeAddOp2(v, OP_Affinity, base, n);

     sqlite3IndexAffinityStr(v, pIdx);

     sqlite3ExprCacheAffinityChange(pParse, base, n);

   }

 }

 /*

 ** Generate code for a single equality term of the WHERE clause.  An equality

 ** term can be either X=expr or X IN (...).   pTerm is the term to be 

 ** coded.

 **

 ** The current value for the constraint is left in register iReg.

 **

 ** For a constraint of the form X=expr, the expression is evaluated and its

 ** result is left on the stack.  For constraints of the form X IN (...)

 ** this routine sets up a loop that will iterate over all values of X.

 */

 static int codeEqualityTerm(

   Parse *pParse,      /* The parsing context */

   WhereTerm *pTerm,   /* The term of the WHERE clause to be coded */

   WhereLevel *pLevel, /* When level of the FROM clause we are working on */

   int iTarget         /* Attempt to leave results in this register */

 ){

   Expr *pX = pTerm->pExpr;

   Vdbe *v = pParse->pVdbe;

   int iReg;                  /* Register holding results */

   if( iTarget<=0 ){

     iReg = iTarget = sqlite3GetTempReg(pParse);

   }

   if( pX->op==TK_EQ ){

     iReg = sqlite3ExprCodeTarget(pParse, pX->pRight, iTarget);

   }else if( pX->op==TK_ISNULL ){

     iReg = iTarget;

     sqlite3VdbeAddOp2(v, OP_Null, 0, iReg);

 #ifndef SQLITE_OMIT_SUBQUERY

   }else{

     int eType;

     int iTab;

     struct InLoop *pIn;

     assert( pX->op==TK_IN );

     iReg = iTarget;

     eType = sqlite3FindInIndex(pParse, pX, 0);

     iTab = pX->iTable;

     sqlite3VdbeAddOp2(v, OP_Rewind, iTab, 0);

     VdbeComment((v, "%.*s", pX->span.n, pX->span.z));

     if( pLevel->nIn==0 ){

       pLevel->nxt = sqlite3VdbeMakeLabel(v);

     }

     pLevel->nIn++;

     pLevel->aInLoop = sqlite3DbReallocOrFree(pParse->db, pLevel->aInLoop,

                                     sizeof(pLevel->aInLoop[0])*pLevel->nIn);

     pIn = pLevel->aInLoop;

     if( pIn ){

       pIn += pLevel->nIn - 1;

       pIn->iCur = iTab;

       if( eType==IN_INDEX_ROWID ){

         pIn->topAddr = sqlite3VdbeAddOp2(v, OP_Rowid, iTab, iReg);

       }else{

         pIn->topAddr = sqlite3VdbeAddOp3(v, OP_Column, iTab, 0, iReg);

       }

       sqlite3VdbeAddOp1(v, OP_IsNull, iReg);

     }else{

       pLevel->nIn = 0;

     }

 #endif

   }

   disableTerm(pLevel, pTerm);

   return iReg;

 }

 /*

 ** Generate code that will evaluate all == and IN constraints for an

 ** index.  The values for all constraints are left on the stack.

 **

 ** For example, consider table t1(a,b,c,d,e,f) with index i1(a,b,c).

 ** Suppose the WHERE clause is this:  a==5 AND b IN (1,2,3) AND c>5 AND c<10

 ** The index has as many as three equality constraints, but in this

 ** example, the third "c" value is an inequality.  So only two 

 ** constraints are coded.  This routine will generate code to evaluate

 ** a==5 and b IN (1,2,3).  The current values for a and b will be left

 ** on the stack - a is the deepest and b the shallowest.

 **

 ** In the example above nEq==2.  But this subroutine works for any value

 ** of nEq including 0.  If nEq==0, this routine is nearly a no-op.

 ** The only thing it does is allocate the pLevel->iMem memory cell.

 **

 ** This routine always allocates at least one memory cell and puts

 ** the address of that memory cell in pLevel->iMem.  The code that

 ** calls this routine will use pLevel->iMem to store the termination

 ** key value of the loop.  If one or more IN operators appear, then

 ** this routine allocates an additional nEq memory cells for internal

 ** use.

 */

 static int codeAllEqualityTerms(

   Parse *pParse,        /* Parsing context */

   WhereLevel *pLevel,   /* Which nested loop of the FROM we are coding */

   WhereClause *pWC,     /* The WHERE clause */

   Bitmask notReady,     /* Which parts of FROM have not yet been coded */

   int nExtraReg         /* Number of extra registers to allocate */

 ){

   int nEq = pLevel->nEq;        /* The number of == or IN constraints to code */

   Vdbe *v = pParse->pVdbe;      /* The virtual machine under construction */

   Index *pIdx = pLevel->pIdx;   /* The index being used for this loop */

   int iCur = pLevel->iTabCur;   /* The cursor of the table */

   WhereTerm *pTerm;             /* A single constraint term */

   int j;                        /* Loop counter */

   int regBase;                  /* Base register */

   /* Figure out how many memory cells we will need then allocate them.

   ** We always need at least one used to store the loop terminator

   ** value.  If there are IN operators we'll need one for each == or

   ** IN constraint.

   */

   pLevel->iMem = pParse->nMem + 1;

   regBase = pParse->nMem + 2;

   pParse->nMem += pLevel->nEq + 2 + nExtraReg;

   /* Evaluate the equality constraints

   */

   assert( pIdx->nColumn>=nEq );

   for(j=0; j<nEq; j++){

     int r1;

     int k = pIdx->aiColumn[j];

     pTerm = findTerm(pWC, iCur, k, notReady, pLevel->flags, pIdx);

     if( NEVER(pTerm==0) ) break;

     assert( (pTerm->flags & TERM_CODED)==0 );

     r1 = codeEqualityTerm(pParse, pTerm, pLevel, regBase+j);

     if( r1!=regBase+j ){

       sqlite3VdbeAddOp2(v, OP_SCopy, r1, regBase+j);

     }

     testcase( pTerm->eOperator & WO_ISNULL );

     testcase( pTerm->eOperator & WO_IN );

     if( (pTerm->eOperator & (WO_ISNULL|WO_IN))==0 ){

       sqlite3VdbeAddOp2(v, OP_IsNull, regBase+j, pLevel->brk);

     }

   }

   return regBase;

 }

 #if defined(SQLITE_TEST)

 /*

 ** The following variable holds a text description of query plan generated

 ** by the most recent call to sqlite3WhereBegin().  Each call to WhereBegin

 ** overwrites the previous.  This information is used for testing and

 ** analysis only.

 */

 char sqlite3_query_plan[BMS*2*40];  /* Text of the join */

 static int nQPlan = 0;              /* Next free slow in _query_plan[] */

 #endif /* SQLITE_TEST */

 /*

 ** Free a WhereInfo structure

 */

 static void whereInfoFree(WhereInfo *pWInfo){

   if( pWInfo ){

     int i;

     sqlite3 *db = pWInfo->pParse->db;

     for(i=0; i<pWInfo->nLevel; i++){

       sqlite3_index_info *pInfo = pWInfo->a[i].pIdxInfo;

       if( pInfo ){

         assert( pInfo->needToFreeIdxStr==0 );

         sqlite3DbFree(db, pInfo);

       }

     }

     sqlite3DbFree(db, pWInfo);

   }

 }

 /*

 ** Generate the beginning of the loop used for WHERE clause processing.

 ** The return value is a pointer to an opaque structure that contains

 ** information needed to terminate the loop.  Later, the calling routine

 ** should invoke sqlite3WhereEnd() with the return value of this function

 ** in order to complete the WHERE clause processing.

 **

 ** If an error occurs, this routine returns NULL.

 **

 ** The basic idea is to do a nested loop, one loop for each table in

 ** the FROM clause of a select.  (INSERT and UPDATE statements are the

 ** same as a SELECT with only a single table in the FROM clause.)  For

 ** example, if the SQL is this:

 **

 **       SELECT * FROM t1, t2, t3 WHERE ...;

 **

 ** Then the code generated is conceptually like the following:

 **

 **      foreach row1 in t1 do       \    Code generated

 **        foreach row2 in t2 do      |-- by sqlite3WhereBegin()

 **          foreach row3 in t3 do   /

 **            ...

 **          end                     \    Code generated

 **        end                        |-- by sqlite3WhereEnd()

 **      end                         /

 **

 ** Note that the loops might not be nested in the order in which they

 ** appear in the FROM clause if a different order is better able to make

 ** use of indices.  Note also that when the IN operator appears in

 ** the WHERE clause, it might result in additional nested loops for

 ** scanning through all values on the right-hand side of the IN.

 **

 ** There are Btree cursors associated with each table.  t1 uses cursor

 ** number pTabList->a[0].iCursor.  t2 uses the cursor pTabList->a[1].iCursor.

 ** And so forth.  This routine generates code to open those VDBE cursors

 ** and sqlite3WhereEnd() generates the code to close them.

 **

 ** The code that sqlite3WhereBegin() generates leaves the cursors named

 ** in pTabList pointing at their appropriate entries.  The [...] code

 ** can use OP_Column and OP_Rowid opcodes on these cursors to extract

 ** data from the various tables of the loop.

 **

 ** If the WHERE clause is empty, the foreach loops must each scan their

 ** entire tables.  Thus a three-way join is an O(N^3) operation.  But if

 ** the tables have indices and there are terms in the WHERE clause that

 ** refer to those indices, a complete table scan can be avoided and the

 ** code will run much faster.  Most of the work of this routine is checking

 ** to see if there are indices that can be used to speed up the loop.

 **

 ** Terms of the WHERE clause are also used to limit which rows actually

 ** make it to the "..." in the middle of the loop.  After each "foreach",

 ** terms of the WHERE clause that use only terms in that loop and outer

 ** loops are evaluated and if false a jump is made around all subsequent

 ** inner loops (or around the "..." if the test occurs within the inner-

 ** most loop)

 **

 ** OUTER JOINS

 **

 ** An outer join of tables t1 and t2 is conceptally coded as follows:

 **

 **    foreach row1 in t1 do

 **      flag = 0

 **      foreach row2 in t2 do

 **        start:

 **          ...

 **          flag = 1

 **      end

 **      if flag==0 then

 **        move the row2 cursor to a null row

 **        goto start

 **      fi

 **    end

 **

 ** ORDER BY CLAUSE PROCESSING

 **

 ** *ppOrderBy is a pointer to the ORDER BY clause of a SELECT statement,

 ** if there is one.  If there is no ORDER BY clause or if this routine

 ** is called from an UPDATE or DELETE statement, then ppOrderBy is NULL.

 **

 ** If an index can be used so that the natural output order of the table

 ** scan is correct for the ORDER BY clause, then that index is used and

 ** *ppOrderBy is set to NULL.  This is an optimization that prevents an

 ** unnecessary sort of the result set if an index appropriate for the

 ** ORDER BY clause already exists.

 **

 ** If the where clause loops cannot be arranged to provide the correct

 ** output order, then the *ppOrderBy is unchanged.

 */

 WhereInfo *sqlite3WhereBegin(

   Parse *pParse,        /* The parser context */

   SrcList *pTabList,    /* A list of all tables to be scanned */

   Expr *pWhere,         /* The WHERE clause */

   ExprList **ppOrderBy, /* An ORDER BY clause, or NULL */

   u8 wflags             /* One of the WHERE_* flags defined in sqliteInt.h */

 ){

   int i;                     /* Loop counter */

   WhereInfo *pWInfo;         /* Will become the return value of this function */

   Vdbe *v = pParse->pVdbe;   /* The virtual database engine */

   int brk, cont = 0;         /* Addresses used during code generation */

   Bitmask notReady;          /* Cursors that are not yet positioned */

   WhereTerm *pTerm;          /* A single term in the WHERE clause */

   ExprMaskSet maskSet;       /* The expression mask set */

   WhereClause wc;            /* The WHERE clause is divided into these terms */

   struct SrcList_item *pTabItem;  /* A single entry from pTabList */

   WhereLevel *pLevel;             /* A single level in the pWInfo list */

   int iFrom;                      /* First unused FROM clause element */

   int andFlags;              /* AND-ed combination of all wc.a[].flags */

   sqlite3 *db;               /* Database connection */

   ExprList *pOrderBy = 0;

   /* The number of tables in the FROM clause is limited by the number of

   ** bits in a Bitmask 

   */

   if( pTabList->nSrc>BMS ){

     sqlite3ErrorMsg(pParse, "at most %d tables in a join", BMS);

     return 0;

   }

   if( ppOrderBy ){

     pOrderBy = *ppOrderBy;

   }

   /* Split the WHERE clause into separate subexpressions where each

   ** subexpression is separated by an AND operator.

   */

   initMaskSet(&maskSet);

   whereClauseInit(&wc, pParse, &maskSet);

   sqlite3ExprCodeConstants(pParse, pWhere);

   whereSplit(&wc, pWhere, TK_AND);

   /* Allocate and initialize the WhereInfo structure that will become the

   ** return value.

   */

   db = pParse->db;

   pWInfo = sqlite3DbMallocZero(db,  

                       sizeof(WhereInfo) + pTabList->nSrc*sizeof(WhereLevel));

   if( db->mallocFailed ){

     goto whereBeginNoMem;

   }

   pWInfo->nLevel = pTabList->nSrc;

   pWInfo->pParse = pParse;

   pWInfo->pTabList = pTabList;

   pWInfo->iBreak = sqlite3VdbeMakeLabel(v);

   /* Special case: a WHERE clause that is constant.  Evaluate the

   ** expression and either jump over all of the code or fall thru.

   */

   if( pWhere && (pTabList->nSrc==0 || sqlite3ExprIsConstantNotJoin(pWhere)) ){

     sqlite3ExprIfFalse(pParse, pWhere, pWInfo->iBreak, SQLITE_JUMPIFNULL);

     pWhere = 0;

   }

   /* Assign a bit from the bitmask to every term in the FROM clause.

   **

   ** When assigning bitmask values to FROM clause cursors, it must be

   ** the case that if X is the bitmask for the N-th FROM clause term then

   ** the bitmask for all FROM clause terms to the left of the N-th term

   ** is (X-1).   An expression from the ON clause of a LEFT JOIN can use

   ** its Expr.iRightJoinTable value to find the bitmask of the right table

   ** of the join.  Subtracting one from the right table bitmask gives a

   ** bitmask for all tables to the left of the join.  Knowing the bitmask

   ** for all tables to the left of a left join is important.  Ticket #3015.

   */

   for(i=0; i<pTabList->nSrc; i++){

     createMask(&maskSet, pTabList->a[i].iCursor);

   }

 #ifndef NDEBUG

   {

     Bitmask toTheLeft = 0;

     for(i=0; i<pTabList->nSrc; i++){

       Bitmask m = getMask(&maskSet, pTabList->a[i].iCursor);

       assert( (m-1)==toTheLeft );

       toTheLeft |= m;

     }

   }

 #endif

   /* Analyze all of the subexpressions.  Note that exprAnalyze() might

   ** add new virtual terms onto the end of the WHERE clause.  We do not

   ** want to analyze these virtual terms, so start analyzing at the end

   ** and work forward so that the added virtual terms are never processed.

   */

   exprAnalyzeAll(pTabList, &wc);

   if( db->mallocFailed ){

     goto whereBeginNoMem;

   }

   /* Chose the best index to use for each table in the FROM clause.

   **

   ** This loop fills in the following fields:

   **

   **   pWInfo->a[].pIdx      The index to use for this level of the loop.

   **   pWInfo->a[].flags     WHERE_xxx flags associated with pIdx

   **   pWInfo->a[].nEq       The number of == and IN constraints

   **   pWInfo->a[].iFrom     When term of the FROM clause is being coded

   **   pWInfo->a[].iTabCur   The VDBE cursor for the database table

   **   pWInfo->a[].iIdxCur   The VDBE cursor for the index

   **

   ** This loop also figures out the nesting order of tables in the FROM

   ** clause.

   */

   notReady = ~(Bitmask)0;

   pTabItem = pTabList->a;

   pLevel = pWInfo->a;

   andFlags = ~0;

   WHERETRACE(("*** Optimizer Start ***\n"));

   for(i=iFrom=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){

     Index *pIdx;                /* Index for FROM table at pTabItem */

     int flags;                  /* Flags asssociated with pIdx */

     int nEq;                    /* Number of == or IN constraints */

     double cost;                /* The cost for pIdx */

     int j;                      /* For looping over FROM tables */

     Index *pBest = 0;           /* The best index seen so far */

     int bestFlags = 0;          /* Flags associated with pBest */

     int bestNEq = 0;            /* nEq associated with pBest */

     double lowestCost;          /* Cost of the pBest */

     int bestJ = 0;              /* The value of j */

     Bitmask m;                  /* Bitmask value for j or bestJ */

     int once = 0;               /* True when first table is seen */

     sqlite3_index_info *pIndex; /* Current virtual index */

     lowestCost = SQLITE_BIG_DBL;

     for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){

       int doNotReorder;  /* True if this table should not be reordered */

       doNotReorder =  (pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0;

       if( once && doNotReorder ) break;

       m = getMask(&maskSet, pTabItem->iCursor);

       if( (m & notReady)==0 ){

         if( j==iFrom ) iFrom++;

         continue;

       }

       assert( pTabItem->pTab );

 #ifndef SQLITE_OMIT_VIRTUALTABLE

       if( IsVirtual(pTabItem->pTab) ){

         sqlite3_index_info **ppIdxInfo = &pWInfo->a[j].pIdxInfo;

         cost = bestVirtualIndex(pParse, &wc, pTabItem, notReady,

                                 ppOrderBy ? *ppOrderBy : 0, i==0,

                                 ppIdxInfo);

         flags = WHERE_VIRTUALTABLE;

         pIndex = *ppIdxInfo;

         if( pIndex && pIndex->orderByConsumed ){

           flags = WHERE_VIRTUALTABLE | WHERE_ORDERBY;

         }

         pIdx = 0;

         nEq = 0;

         if( (SQLITE_BIG_DBL/2.0)<cost ){

           /* The cost is not allowed to be larger than SQLITE_BIG_DBL (the

           ** inital value of lowestCost in this loop. If it is, then

           ** the (cost<lowestCost) test below will never be true and

           ** pLevel->pBestIdx never set.

           */ 

           cost = (SQLITE_BIG_DBL/2.0);

         }

       }else 

 #endif

       {

         cost = bestIndex(pParse, &wc, pTabItem, notReady,

                          (i==0 && ppOrderBy) ? *ppOrderBy : 0,

                          &pIdx, &flags, &nEq);

         pIndex = 0;

       }

       if( cost<lowestCost ){

         once = 1;

         lowestCost = cost;

         pBest = pIdx;

         bestFlags = flags;

         bestNEq = nEq;

         bestJ = j;

         pLevel->pBestIdx = pIndex;

       }

       if( doNotReorder ) break;

     }

     WHERETRACE(("*** Optimizer selects table %d for loop %d\n", bestJ,

            pLevel-pWInfo->a));

     if( (bestFlags & WHERE_ORDERBY)!=0 ){

       *ppOrderBy = 0;

     }

     andFlags &= bestFlags;

     pLevel->flags = bestFlags;

     pLevel->pIdx = pBest;

     pLevel->nEq = bestNEq;

     pLevel->aInLoop = 0;

     pLevel->nIn = 0;

     if( pBest ){

       pLevel->iIdxCur = pParse->nTab++;

     }else{

       pLevel->iIdxCur = -1;

     }

     notReady &= ~getMask(&maskSet, pTabList->a[bestJ].iCursor);

     pLevel->iFrom = bestJ;

   }

   WHERETRACE(("*** Optimizer Finished ***\n"));

   /* If the total query only selects a single row, then the ORDER BY

   ** clause is irrelevant.

   */

   if( (andFlags & WHERE_UNIQUE)!=0 && ppOrderBy ){

     *ppOrderBy = 0;

   }

   /* If the caller is an UPDATE or DELETE statement that is requesting

   ** to use a one-pass algorithm, determine if this is appropriate.

   ** The one-pass algorithm only works if the WHERE clause constraints

   ** the statement to update a single row.

   */

   assert( (wflags & WHERE_ONEPASS_DESIRED)==0 || pWInfo->nLevel==1 );

   if( (wflags & WHERE_ONEPASS_DESIRED)!=0 && (andFlags & WHERE_UNIQUE)!=0 ){

     pWInfo->okOnePass = 1;

     pWInfo->a[0].flags &= ~WHERE_IDX_ONLY;

   }

   /* Open all tables in the pTabList and any indices selected for

   ** searching those tables.

   */

   sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */

   for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){

     Table *pTab;     /* Table to open */

     Index *pIx;      /* Index used to access pTab (if any) */

     int iDb;         /* Index of database containing table/index */

     int iIdxCur = pLevel->iIdxCur;

 #ifndef SQLITE_OMIT_EXPLAIN

     if( pParse->explain==2 ){

       char *zMsg;

       struct SrcList_item *pItem = &pTabList->a[pLevel->iFrom];

       zMsg = sqlite3MPrintf(db, "TABLE %s", pItem->zName);

       if( pItem->zAlias ){

         zMsg = sqlite3MAppendf(db, zMsg, "%s AS %s", zMsg, pItem->zAlias);

       }

       if( (pIx = pLevel->pIdx)!=0 ){

         zMsg = sqlite3MAppendf(db, zMsg, "%s WITH INDEX %s", zMsg, pIx->zName);

       }else if( pLevel->flags & (WHERE_ROWID_EQ|WHERE_ROWID_RANGE) ){

         zMsg = sqlite3MAppendf(db, zMsg, "%s USING PRIMARY KEY", zMsg);

       }

 #ifndef SQLITE_OMIT_VIRTUALTABLE

       else if( pLevel->pBestIdx ){

         sqlite3_index_info *pBestIdx = pLevel->pBestIdx;

         zMsg = sqlite3MAppendf(db, zMsg, "%s VIRTUAL TABLE INDEX %d:%s", zMsg,

                     pBestIdx->idxNum, pBestIdx->idxStr);

       }

 #endif

       if( pLevel->flags & WHERE_ORDERBY ){

         zMsg = sqlite3MAppendf(db, zMsg, "%s ORDER BY", zMsg);

       }

       sqlite3VdbeAddOp4(v, OP_Explain, i, pLevel->iFrom, 0, zMsg, P4_DYNAMIC);

     }

 #endif /* SQLITE_OMIT_EXPLAIN */

     pTabItem = &pTabList->a[pLevel->iFrom];

     pTab = pTabItem->pTab;

     iDb = sqlite3SchemaToIndex(pParse->db, pTab->pSchema);

     if( pTab->isEphem || pTab->pSelect ) continue;

 #ifndef SQLITE_OMIT_VIRTUALTABLE

     if( pLevel->pBestIdx ){

       int iCur = pTabItem->iCursor;

       sqlite3VdbeAddOp4(v, OP_VOpen, iCur, 0, 0,

                         (const char*)pTab->pVtab, P4_VTAB);

     }else

 #endif

     if( (pLevel->flags & WHERE_IDX_ONLY)==0 ){

       int op = pWInfo->okOnePass ? OP_OpenWrite : OP_OpenRead;

       sqlite3OpenTable(pParse, pTabItem->iCursor, iDb, pTab, op);

       if( !pWInfo->okOnePass && pTab->nCol<(sizeof(Bitmask)*8) ){

         Bitmask b = pTabItem->colUsed;

         int n = 0;

         for(; b; b=b>>1, n++){}

         sqlite3VdbeChangeP2(v, sqlite3VdbeCurrentAddr(v)-2, n);

         assert( n<=pTab->nCol );

       }

     }else{

       sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);

     }

     pLevel->iTabCur = pTabItem->iCursor;

     if( (pIx = pLevel->pIdx)!=0 ){

       KeyInfo *pKey = sqlite3IndexKeyinfo(pParse, pIx);

       assert( pIx->pSchema==pTab->pSchema );

       sqlite3VdbeAddOp2(v, OP_SetNumColumns, 0, pIx->nColumn+1);

       sqlite3VdbeAddOp4(v, OP_OpenRead, iIdxCur, pIx->tnum, iDb,

                         (char*)pKey, P4_KEYINFO_HANDOFF);

       VdbeComment((v, "%s", pIx->zName));

     }

     sqlite3CodeVerifySchema(pParse, iDb);

   }

   pWInfo->iTop = sqlite3VdbeCurrentAddr(v);

   /* Generate the code to do the search.  Each iteration of the for

   ** loop below generates code for a single nested loop of the VM

   ** program.

   */

   notReady = ~(Bitmask)0;

   for(i=0, pLevel=pWInfo->a; i<pTabList->nSrc; i++, pLevel++){

     int j;

     int iCur = pTabItem->iCursor;  /* The VDBE cursor for the table */

     Index *pIdx;       /* The index we will be using */

     int nxt;           /* Where to jump to continue with the next IN case */

     int iIdxCur;       /* The VDBE cursor for the index */

     int omitTable;     /* True if we use the index only */

     int bRev;          /* True if we need to scan in reverse order */

     pTabItem = &pTabList->a[pLevel->iFrom];

     iCur = pTabItem->iCursor;

     pIdx = pLevel->pIdx;

     iIdxCur = pLevel->iIdxCur;

     bRev = (pLevel->flags & WHERE_REVERSE)!=0;

     omitTable = (pLevel->flags & WHERE_IDX_ONLY)!=0;

     /* Create labels for the "break" and "continue" instructions

     ** for the current loop.  Jump to brk to break out of a loop.

     ** Jump to cont to go immediately to the next iteration of the

     ** loop.

     **

     ** When there is an IN operator, we also have a "nxt" label that

     ** means to continue with the next IN value combination.  When

     ** there are no IN operators in the constraints, the "nxt" label

     ** is the same as "brk".

     */

     brk = pLevel->brk = pLevel->nxt = sqlite3VdbeMakeLabel(v);

     cont = pLevel->cont = sqlite3VdbeMakeLabel(v);

     /* If this is the right table of a LEFT OUTER JOIN, allocate and

     ** initialize a memory cell that records if this table matches any

     ** row of the left table of the join.

     */

     if( pLevel->iFrom>0 && (pTabItem[0].jointype & JT_LEFT)!=0 ){

       pLevel->iLeftJoin = ++pParse->nMem;

       sqlite3VdbeAddOp2(v, OP_Integer, 0, pLevel->iLeftJoin);

       VdbeComment((v, "init LEFT JOIN no-match flag"));

     }

 #ifndef SQLITE_OMIT_VIRTUALTABLE

     if( pLevel->pBestIdx ){

       /* Case 0:  The table is a virtual-table.  Use the VFilter and VNext

       **          to access the data.

       */

       int j;

       int iReg;   /* P3 Value for OP_VFilter */

       sqlite3_index_info *pBestIdx = pLevel->pBestIdx;

       int nConstraint = pBestIdx->nConstraint;

       struct sqlite3_index_constraint_usage *aUsage =

                                                   pBestIdx->aConstraintUsage;

       const struct sqlite3_index_constraint *aConstraint =

                                                   pBestIdx->aConstraint;

       iReg = sqlite3GetTempRange(pParse, nConstraint+2);

       pParse->disableColCache++;

       for(j=1; j<=nConstraint; j++){

         int k;

         for(k=0; k<nConstraint; k++){

           if( aUsage[k].argvIndex==j ){

             int iTerm = aConstraint[k].iTermOffset;

             assert( pParse->disableColCache );

             sqlite3ExprCode(pParse, wc.a[iTerm].pExpr->pRight, iReg+j+1);

             break;

           }

         }

         if( k==nConstraint ) break;

       }

       assert( pParse->disableColCache );

       pParse->disableColCache--;

       sqlite3VdbeAddOp2(v, OP_Integer, pBestIdx->idxNum, iReg);

       sqlite3VdbeAddOp2(v, OP_Integer, j-1, iReg+1);

       sqlite3VdbeAddOp4(v, OP_VFilter, iCur, brk, iReg, pBestIdx->idxStr,

                         pBestIdx->needToFreeIdxStr ? P4_MPRINTF : P4_STATIC);

       sqlite3ReleaseTempRange(pParse, iReg, nConstraint+2);

       pBestIdx->needToFreeIdxStr = 0;

       for(j=0; j<nConstraint; j++){

         if( aUsage[j].omit ){

           int iTerm = aConstraint[j].iTermOffset;

           disableTerm(pLevel, &wc.a[iTerm]);

         }

       }

       pLevel->op = OP_VNext;

       pLevel->p1 = iCur;

       pLevel->p2 = sqlite3VdbeCurrentAddr(v);

     }else

 #endif /* SQLITE_OMIT_VIRTUALTABLE */

     if( pLevel->flags & WHERE_ROWID_EQ ){

       /* Case 1:  We can directly reference a single row using an

       **          equality comparison against the ROWID field.  Or

       **          we reference multiple rows using a "rowid IN (...)"

       **          construct.

       */

       int r1;

       pTerm = findTerm(&wc, iCur, -1, notReady, WO_EQ|WO_IN, 0);

       assert( pTerm!=0 );

       assert( pTerm->pExpr!=0 );

       assert( pTerm->leftCursor==iCur );

       assert( omitTable==0 );

       r1 = codeEqualityTerm(pParse, pTerm, pLevel, 0);

       nxt = pLevel->nxt;

       sqlite3VdbeAddOp2(v, OP_MustBeInt, r1, nxt);

       sqlite3VdbeAddOp3(v, OP_NotExists, iCur, nxt, r1);

       VdbeComment((v, "pk"));

       pLevel->op = OP_Noop;

     }else if( pLevel->flags & WHERE_ROWID_RANGE ){

       /* Case 2:  We have an inequality comparison against the ROWID field.

       */

       int testOp = OP_Noop;

       int start;

       WhereTerm *pStart, *pEnd;

       assert( omitTable==0 );

       pStart = findTerm(&wc, iCur, -1, notReady, WO_GT|WO_GE, 0);

       pEnd = findTerm(&wc, iCur, -1, notReady, WO_LT|WO_LE, 0);

       if( bRev ){

         pTerm = pStart;

         pStart = pEnd;

         pEnd = pTerm;

       }

       if( pStart ){

         Expr *pX;

         int r1, regFree1;

         pX = pStart->pExpr;

         assert( pX!=0 );

         assert( pStart->leftCursor==iCur );

         r1 = sqlite3ExprCodeTemp(pParse, pX->pRight, &regFree1);

         sqlite3VdbeAddOp3(v, OP_ForceInt, r1, brk, 

                              pX->op==TK_LE || pX->op==TK_GT);

         sqlite3VdbeAddOp3(v, bRev ? OP_MoveLt : OP_MoveGe, iCur, brk, r1);

         VdbeComment((v, "pk"));

         sqlite3ReleaseTempReg(pParse, regFree1);

         disableTerm(pLevel, pStart);

       }else{

         sqlite3VdbeAddOp2(v, bRev ? OP_Last : OP_Rewind, iCur, brk);

       }

       if( pEnd ){

         Expr *pX;

         pX = pEnd->pExpr;

         assert( pX!=0 );

         assert( pEnd->leftCursor==iCur );

         pLevel->iMem = ++pParse->nMem;

         sqlite3ExprCode(pParse, pX->pRight, pLevel->iMem);

         if( pX->op==TK_LT || pX->op==TK_GT ){

           testOp = bRev ? OP_Le : OP_Ge;

         }else{

           testOp = bRev ? OP_Lt : OP_Gt;

         }

         disableTerm(pLevel, pEnd);

       }

       start = sqlite3VdbeCurrentAddr(v);

       pLevel->op = bRev ? OP_Prev : OP_Next;

       pLevel->p1 = iCur;

       pLevel->p2 = start;

       if( testOp!=OP_Noop ){

         int r1 = sqlite3GetTempReg(pParse);

         sqlite3VdbeAddOp2(v, OP_Rowid, iCur, r1);

         /* sqlite3VdbeAddOp2(v, OP_SCopy, pLevel->iMem, 0); */

         sqlite3VdbeAddOp3(v, testOp, pLevel->iMem, brk, r1);

         sqlite3VdbeChangeP5(v, SQLITE_AFF_NUMERIC | SQLITE_JUMPIFNULL);

         sqlite3ReleaseTempReg(pParse, r1);

       }

     }else if( pLevel->flags & (WHERE_COLUMN_RANGE|WHERE_COLUMN_EQ) ){

       /* Case 3: A scan using an index.

       **

       **         The WHERE clause may contain zero or more equality 

       **         terms ("==" or "IN" operators) that refer to the N

       **         left-most columns of the index. It may also contain

       **         inequality constraints (>, <, >= or <=) on the indexed

       **         column that immediately follows the N equalities. Only 

       **         the right-most column can be an inequality - the rest must

       **         use the "==" and "IN" operators. For example, if the 

       **         index is on (x,y,z), then the following clauses are all 

       **         optimized:

       **

       **            x=5

       **            x=5 AND y=10

       **            x=5 AND y<10

       **            x=5 AND y>5 AND y<10

       **            x=5 AND y=5 AND z<=10

       **

       **         The z<10 term of the following cannot be used, only

       **         the x=5 term:

       **

       **            x=5 AND z<10

       **

       **         N may be zero if there are inequality constraints.

       **         If there are no inequality constraints, then N is at

       **         least one.

       **

       **         This case is also used when there are no WHERE clause

       **         constraints but an index is selected anyway, in order

       **         to force the output order to conform to an ORDER BY.

       */  

       int aStartOp[] = {

         0,

         0,

         OP_Rewind,           /* 2: (!start_constraints && startEq &&  !bRev) */

         OP_Last,             /* 3: (!start_constraints && startEq &&   bRev) */

         OP_MoveGt,           /* 4: (start_constraints  && !startEq && !bRev) */

         OP_MoveLt,           /* 5: (start_constraints  && !startEq &&  bRev) */

         OP_MoveGe,           /* 6: (start_constraints  &&  startEq && !bRev) */

         OP_MoveLe            /* 7: (start_constraints  &&  startEq &&  bRev) */

       };

       int aEndOp[] = {

         OP_Noop,             /* 0: (!end_constraints) */

         OP_IdxGE,            /* 1: (end_constraints && !bRev) */

         OP_IdxLT             /* 2: (end_constraints && bRev) */

       };

       int nEq = pLevel->nEq;

       int isMinQuery = 0;          /* If this is an optimized SELECT min(x).. */

       int regBase;                 /* Base register holding constraint values */

       int r1;                      /* Temp register */

       WhereTerm *pRangeStart = 0;  /* Inequality constraint at range start */

       WhereTerm *pRangeEnd = 0;    /* Inequality constraint at range end */

       int startEq;                 /* True if range start uses ==, >= or <= */

       int endEq;                   /* True if range end uses ==, >= or <= */

       int start_constraints;       /* Start of range is constrained */

       int k = pIdx->aiColumn[nEq]; /* Column for inequality constraints */

       int nConstraint;             /* Number of constraint terms */

       int op;

       /* Generate code to evaluate all constraint terms using == or IN

       ** and store the values of those terms in an array of registers

       ** starting at regBase.

       */

       regBase = codeAllEqualityTerms(pParse, pLevel, &wc, notReady, 2);

       nxt = pLevel->nxt;

       /* If this loop satisfies a sort order (pOrderBy) request that 

       ** was passed to this function to implement a "SELECT min(x) ..." 

       ** query, then the caller will only allow the loop to run for

       ** a single iteration. This means that the first row returned

       ** should not have a NULL value stored in 'x'. If column 'x' is

       ** the first one after the nEq equality constraints in the index,

       ** this requires some special handling.

       */

       if( (wflags&WHERE_ORDERBY_MIN)!=0

        && (pLevel->flags&WHERE_ORDERBY)

        && (pIdx->nColumn>nEq)

       ){

         assert( pOrderBy->nExpr==1 );

         assert( pOrderBy->a[0].pExpr->iColumn==pIdx->aiColumn[nEq] );

         isMinQuery = 1;

       }

       /* Find any inequality constraint terms for the start and end 

       ** of the range. 

       */

       if( pLevel->flags & WHERE_TOP_LIMIT ){

         pRangeEnd = findTerm(&wc, iCur, k, notReady, (WO_LT|WO_LE), pIdx);

       }

       if( pLevel->flags & WHERE_BTM_LIMIT ){

         pRangeStart = findTerm(&wc, iCur, k, notReady, (WO_GT|WO_GE), pIdx);

       }

       /* If we are doing a reverse order scan on an ascending index, or

       ** a forward order scan on a descending index, interchange the 

       ** start and end terms (pRangeStart and pRangeEnd).

       */

       if( bRev==(pIdx->aSortOrder[nEq]==SQLITE_SO_ASC) ){

         SWAP(WhereTerm *, pRangeEnd, pRangeStart);

       }

       testcase( pRangeStart && pRangeStart->eOperator & WO_LE );

       testcase( pRangeStart && pRangeStart->eOperator & WO_GE );

       testcase( pRangeEnd && pRangeEnd->eOperator & WO_LE );

       testcase( pRangeEnd && pRangeEnd->eOperator & WO_GE );

       startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);

       endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);

       start_constraints = pRangeStart || nEq>0;

       /* Seek the index cursor to the start of the range. */

       nConstraint = nEq;

       if( pRangeStart ){

         int dcc = pParse->disableColCache;

         if( pRangeEnd ){

           pParse->disableColCache++;

         }

         sqlite3ExprCode(pParse, pRangeStart->pExpr->pRight, regBase+nEq);

         pParse->disableColCache = dcc;

         sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, nxt);

         nConstraint++;

       }else if( isMinQuery ){

         sqlite3VdbeAddOp2(v, OP_Null, 0, regBase+nEq);

         nConstraint++;

         startEq = 0;

         start_constraints = 1;

       }

       codeApplyAffinity(pParse, regBase, nConstraint, pIdx);

       op = aStartOp[(start_constraints<<2) + (startEq<<1) + bRev];

       assert( op!=0 );

       testcase( op==OP_Rewind );

       testcase( op==OP_Last );

       testcase( op==OP_MoveGt );

       testcase( op==OP_MoveGe );

       testcase( op==OP_MoveLe );

       testcase( op==OP_MoveLt );

       sqlite3VdbeAddOp4(v, op, iIdxCur, nxt, regBase, 

                         SQLITE_INT_TO_PTR(nConstraint), P4_INT32);

       /* Load the value for the inequality constraint at the end of the

       ** range (if any).

       */

       nConstraint = nEq;

       if( pRangeEnd ){

         sqlite3ExprCode(pParse, pRangeEnd->pExpr->pRight, regBase+nEq);

         sqlite3VdbeAddOp2(v, OP_IsNull, regBase+nEq, nxt);

         codeApplyAffinity(pParse, regBase, nEq+1, pIdx);

         nConstraint++;

       }

       /* Top of the loop body */

       pLevel->p2 = sqlite3VdbeCurrentAddr(v);

       /* Check if the index cursor is past the end of the range. */

       op = aEndOp[(pRangeEnd || nEq) * (1 + bRev)];

       testcase( op==OP_Noop );

       testcase( op==OP_IdxGE );

       testcase( op==OP_IdxLT );

       sqlite3VdbeAddOp4(v, op, iIdxCur, nxt, regBase,

                         SQLITE_INT_TO_PTR(nConstraint), P4_INT32);

       sqlite3VdbeChangeP5(v, endEq!=bRev);

       /* If there are inequality constraints, check that the value

       ** of the table column that the inequality contrains is not NULL.

       ** If it is, jump to the next iteration of the loop.

       */

       r1 = sqlite3GetTempReg(pParse);

       testcase( pLevel->flags & WHERE_BTM_LIMIT );

       testcase( pLevel->flags & WHERE_TOP_LIMIT );

       if( pLevel->flags & (WHERE_BTM_LIMIT|WHERE_TOP_LIMIT) ){

         sqlite3VdbeAddOp3(v, OP_Column, iIdxCur, nEq, r1);

         sqlite3VdbeAddOp2(v, OP_IsNull, r1, cont);