/*

 ** 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 file contains C code routines that are called by the parser

 ** to handle SELECT statements in SQLite.

 **

 ** $Id: select.c,v 1.480 2008/10/07 19:53:14 drh Exp $

 */

 #include "sqliteInt.h"

 /*

 ** Delete all the content of a Select structure but do not deallocate

 ** the select structure itself.

 */

 static void clearSelect(sqlite3 *db, Select *p){

   sqlite3ExprListDelete(db, p->pEList);

   sqlite3SrcListDelete(db, p->pSrc);

   sqlite3ExprDelete(db, p->pWhere);

   sqlite3ExprListDelete(db, p->pGroupBy);

   sqlite3ExprDelete(db, p->pHaving);

   sqlite3ExprListDelete(db, p->pOrderBy);

   sqlite3SelectDelete(db, p->pPrior);

   sqlite3ExprDelete(db, p->pLimit);

   sqlite3ExprDelete(db, p->pOffset);

 }

 /*

 ** Initialize a SelectDest structure.

 */

 void sqlite3SelectDestInit(SelectDest *pDest, int eDest, int iParm){

   pDest->eDest = eDest;

   pDest->iParm = iParm;

   pDest->affinity = 0;

   pDest->iMem = 0;

   pDest->nMem = 0;

 }

 /*

 ** Allocate a new Select structure and return a pointer to that

 ** structure.

 */

 Select *sqlite3SelectNew(

   Parse *pParse,        /* Parsing context */

   ExprList *pEList,     /* which columns to include in the result */

   SrcList *pSrc,        /* the FROM clause -- which tables to scan */

   Expr *pWhere,         /* the WHERE clause */

   ExprList *pGroupBy,   /* the GROUP BY clause */

   Expr *pHaving,        /* the HAVING clause */

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

   int isDistinct,       /* true if the DISTINCT keyword is present */

   Expr *pLimit,         /* LIMIT value.  NULL means not used */

   Expr *pOffset         /* OFFSET value.  NULL means no offset */

 ){

   Select *pNew;

   Select standin;

   sqlite3 *db = pParse->db;

   pNew = sqlite3DbMallocZero(db, sizeof(*pNew) );

   assert( !pOffset || pLimit );   /* Can't have OFFSET without LIMIT. */

   if( pNew==0 ){

     pNew = &standin;

     memset(pNew, 0, sizeof(*pNew));

   }

   if( pEList==0 ){

     pEList = sqlite3ExprListAppend(pParse, 0, sqlite3Expr(db,TK_ALL,0,0,0), 0);

   }

   pNew->pEList = pEList;

   pNew->pSrc = pSrc;

   pNew->pWhere = pWhere;

   pNew->pGroupBy = pGroupBy;

   pNew->pHaving = pHaving;

   pNew->pOrderBy = pOrderBy;

   pNew->selFlags = isDistinct ? SF_Distinct : 0;

   pNew->op = TK_SELECT;

   pNew->pLimit = pLimit;

   pNew->pOffset = pOffset;

   pNew->addrOpenEphm[0] = -1;

   pNew->addrOpenEphm[1] = -1;

   pNew->addrOpenEphm[2] = -1;

   if( db->mallocFailed ) {

     clearSelect(db, pNew);

     if( pNew!=&standin ) sqlite3DbFree(db, pNew);

     pNew = 0;

   }

   return pNew;

 }

 /*

 ** Delete the given Select structure and all of its substructures.

 */

 void sqlite3SelectDelete(sqlite3 *db, Select *p){

   if( p ){

     clearSelect(db, p);

     sqlite3DbFree(db, p);

   }

 }

 /*

 ** Given 1 to 3 identifiers preceeding the JOIN keyword, determine the

 ** type of join.  Return an integer constant that expresses that type

 ** in terms of the following bit values:

 **

 **     JT_INNER

 **     JT_CROSS

 **     JT_OUTER

 **     JT_NATURAL

 **     JT_LEFT

 **     JT_RIGHT

 **

 ** A full outer join is the combination of JT_LEFT and JT_RIGHT.

 **

 ** If an illegal or unsupported join type is seen, then still return

 ** a join type, but put an error in the pParse structure.

 */

 int sqlite3JoinType(Parse *pParse, Token *pA, Token *pB, Token *pC){

   int jointype = 0;

   Token *apAll[3];

   Token *p;

   static const struct {

     const char zKeyword[8];

     u8 nChar;

     u8 code;

   } keywords[] = {

     { "natural", 7, JT_NATURAL },

     { "left",    4, JT_LEFT|JT_OUTER },

     { "right",   5, JT_RIGHT|JT_OUTER },

     { "full",    4, JT_LEFT|JT_RIGHT|JT_OUTER },

     { "outer",   5, JT_OUTER },

     { "inner",   5, JT_INNER },

     { "cross",   5, JT_INNER|JT_CROSS },

   };

   int i, j;

   apAll[0] = pA;

   apAll[1] = pB;

   apAll[2] = pC;

   for(i=0; i<3 && apAll[i]; i++){

     p = apAll[i];

     for(j=0; j<sizeof(keywords)/sizeof(keywords[0]); j++){

       if( p->n==keywords[j].nChar 

           && sqlite3StrNICmp((char*)p->z, keywords[j].zKeyword, p->n)==0 ){

         jointype |= keywords[j].code;

         break;

       }

     }

     if( j>=sizeof(keywords)/sizeof(keywords[0]) ){

       jointype |= JT_ERROR;

       break;

     }

   }

   if(

      (jointype & (JT_INNER|JT_OUTER))==(JT_INNER|JT_OUTER) ||

      (jointype & JT_ERROR)!=0

   ){

     const char *zSp = " ";

     assert( pB!=0 );

     if( pC==0 ){ zSp++; }

     sqlite3ErrorMsg(pParse, "unknown or unsupported join type: "

        "%T %T%s%T", pA, pB, zSp, pC);

     jointype = JT_INNER;

   }else if( jointype & JT_RIGHT ){

     sqlite3ErrorMsg(pParse, 

       "RIGHT and FULL OUTER JOINs are not currently supported");

     jointype = JT_INNER;

   }

   return jointype;

 }

 /*

 ** Return the index of a column in a table.  Return -1 if the column

 ** is not contained in the table.

 */

 static int columnIndex(Table *pTab, const char *zCol){

   int i;

   for(i=0; i<pTab->nCol; i++){

     if( sqlite3StrICmp(pTab->aCol[i].zName, zCol)==0 ) return i;

   }

   return -1;

 }

 /*

 ** Set the value of a token to a '\000'-terminated string.

 */

 static void setToken(Token *p, const char *z){

   p->z = (u8*)z;

   p->n = z ? strlen(z) : 0;

   p->dyn = 0;

 }

 /*

 ** Set the token to the double-quoted and escaped version of the string pointed

 ** to by z. For example;

 **

 **    {a"bc}  ->  {"a""bc"}

 */

 static void setQuotedToken(Parse *pParse, Token *p, const char *z){

   /* Check if the string appears to be quoted using "..." or `...`

   ** or [...] or '...' or if the string contains any " characters.  

   ** If it does, then record a version of the string with the special

   ** characters escaped.

   */

   const char *z2 = z;

   if( *z2!='[' && *z2!='`' && *z2!='\'' ){

     while( *z2 ){

       if( *z2=='"' ) break;

       z2++;

     }

   }

   if( *z2 ){

     /* String contains " characters - copy and quote the string. */

     p->z = (u8 *)sqlite3MPrintf(pParse->db, "\"%w\"", z);

     if( p->z ){

       p->n = strlen((char *)p->z);

       p->dyn = 1;

     }

   }else{

     /* String contains no " characters - copy the pointer. */

     p->z = (u8*)z;

     p->n = (z2 - z);

     p->dyn = 0;

   }

 }

 /*

 ** Create an expression node for an identifier with the name of zName

 */

 Expr *sqlite3CreateIdExpr(Parse *pParse, const char *zName){

   Token dummy;

   setToken(&dummy, zName);

   return sqlite3PExpr(pParse, TK_ID, 0, 0, &dummy);

 }

 /*

 ** Add a term to the WHERE expression in *ppExpr that requires the

 ** zCol column to be equal in the two tables pTab1 and pTab2.

 */

 static void addWhereTerm(

   Parse *pParse,           /* Parsing context */

   const char *zCol,        /* Name of the column */

   const Table *pTab1,      /* First table */

   const char *zAlias1,     /* Alias for first table.  May be NULL */

   const Table *pTab2,      /* Second table */

   const char *zAlias2,     /* Alias for second table.  May be NULL */

   int iRightJoinTable,     /* VDBE cursor for the right table */

   Expr **ppExpr,           /* Add the equality term to this expression */

   int isOuterJoin          /* True if dealing with an OUTER join */

 ){

   Expr *pE1a, *pE1b, *pE1c;

   Expr *pE2a, *pE2b, *pE2c;

   Expr *pE;

   pE1a = sqlite3CreateIdExpr(pParse, zCol);

   pE2a = sqlite3CreateIdExpr(pParse, zCol);

   if( zAlias1==0 ){

     zAlias1 = pTab1->zName;

   }

   pE1b = sqlite3CreateIdExpr(pParse, zAlias1);

   if( zAlias2==0 ){

     zAlias2 = pTab2->zName;

   }

   pE2b = sqlite3CreateIdExpr(pParse, zAlias2);

   pE1c = sqlite3PExpr(pParse, TK_DOT, pE1b, pE1a, 0);

   pE2c = sqlite3PExpr(pParse, TK_DOT, pE2b, pE2a, 0);

   pE = sqlite3PExpr(pParse, TK_EQ, pE1c, pE2c, 0);

   if( pE && isOuterJoin ){

     ExprSetProperty(pE, EP_FromJoin);

     pE->iRightJoinTable = iRightJoinTable;

   }

   *ppExpr = sqlite3ExprAnd(pParse->db,*ppExpr, pE);

 }

 /*

 ** Set the EP_FromJoin property on all terms of the given expression.

 ** And set the Expr.iRightJoinTable to iTable for every term in the

 ** expression.

 **

 ** The EP_FromJoin property is used on terms of an expression to tell

 ** the LEFT OUTER JOIN processing logic that this term is part of the

 ** join restriction specified in the ON or USING clause and not a part

 ** of the more general WHERE clause.  These terms are moved over to the

 ** WHERE clause during join processing but we need to remember that they

 ** originated in the ON or USING clause.

 **

 ** The Expr.iRightJoinTable tells the WHERE clause processing that the

 ** expression depends on table iRightJoinTable even if that table is not

 ** explicitly mentioned in the expression.  That information is needed

 ** for cases like this:

 **

 **    SELECT * FROM t1 LEFT JOIN t2 ON t1.a=t2.b AND t1.x=5

 **

 ** The where clause needs to defer the handling of the t1.x=5

 ** term until after the t2 loop of the join.  In that way, a

 ** NULL t2 row will be inserted whenever t1.x!=5.  If we do not

 ** defer the handling of t1.x=5, it will be processed immediately

 ** after the t1 loop and rows with t1.x!=5 will never appear in

 ** the output, which is incorrect.

 */

 static void setJoinExpr(Expr *p, int iTable){

   while( p ){

     ExprSetProperty(p, EP_FromJoin);

     p->iRightJoinTable = iTable;

     setJoinExpr(p->pLeft, iTable);

     p = p->pRight;

   } 

 }

 /*

 ** This routine processes the join information for a SELECT statement.

 ** ON and USING clauses are converted into extra terms of the WHERE clause.

 ** NATURAL joins also create extra WHERE clause terms.

 **

 ** The terms of a FROM clause are contained in the Select.pSrc structure.

 ** The left most table is the first entry in Select.pSrc.  The right-most

 ** table is the last entry.  The join operator is held in the entry to

 ** the left.  Thus entry 0 contains the join operator for the join between

 ** entries 0 and 1.  Any ON or USING clauses associated with the join are

 ** also attached to the left entry.

 **

 ** This routine returns the number of errors encountered.

 */

 static int sqliteProcessJoin(Parse *pParse, Select *p){

   SrcList *pSrc;                  /* All tables in the FROM clause */

   int i, j;                       /* Loop counters */

   struct SrcList_item *pLeft;     /* Left table being joined */

   struct SrcList_item *pRight;    /* Right table being joined */

   pSrc = p->pSrc;

   pLeft = &pSrc->a[0];

   pRight = &pLeft[1];

   for(i=0; i<pSrc->nSrc-1; i++, pRight++, pLeft++){

     Table *pLeftTab = pLeft->pTab;

     Table *pRightTab = pRight->pTab;

     int isOuter;

     if( pLeftTab==0 || pRightTab==0 ) continue;

     isOuter = (pRight->jointype & JT_OUTER)!=0;

     /* When the NATURAL keyword is present, add WHERE clause terms for

     ** every column that the two tables have in common.

     */

     if( pRight->jointype & JT_NATURAL ){

       if( pRight->pOn || pRight->pUsing ){

         sqlite3ErrorMsg(pParse, "a NATURAL join may not have "

            "an ON or USING clause", 0);

         return 1;

       }

       for(j=0; j<pLeftTab->nCol; j++){

         char *zName = pLeftTab->aCol[j].zName;

         if( columnIndex(pRightTab, zName)>=0 ){

           addWhereTerm(pParse, zName, pLeftTab, pLeft->zAlias, 

                               pRightTab, pRight->zAlias,

                               pRight->iCursor, &p->pWhere, isOuter);

         }

       }

     }

     /* Disallow both ON and USING clauses in the same join

     */

     if( pRight->pOn && pRight->pUsing ){

       sqlite3ErrorMsg(pParse, "cannot have both ON and USING "

         "clauses in the same join");

       return 1;

     }

     /* Add the ON clause to the end of the WHERE clause, connected by

     ** an AND operator.

     */

     if( pRight->pOn ){

       if( isOuter ) setJoinExpr(pRight->pOn, pRight->iCursor);

       p->pWhere = sqlite3ExprAnd(pParse->db, p->pWhere, pRight->pOn);

       pRight->pOn = 0;

     }

     /* Create extra terms on the WHERE clause for each column named

     ** in the USING clause.  Example: If the two tables to be joined are 

     ** A and B and the USING clause names X, Y, and Z, then add this

     ** to the WHERE clause:    A.X=B.X AND A.Y=B.Y AND A.Z=B.Z

     ** Report an error if any column mentioned in the USING clause is

     ** not contained in both tables to be joined.

     */

     if( pRight->pUsing ){

       IdList *pList = pRight->pUsing;

       for(j=0; j<pList->nId; j++){

         char *zName = pList->a[j].zName;

         if( columnIndex(pLeftTab, zName)<0 || columnIndex(pRightTab, zName)<0 ){

           sqlite3ErrorMsg(pParse, "cannot join using column %s - column "

             "not present in both tables", zName);

           return 1;

         }

         addWhereTerm(pParse, zName, pLeftTab, pLeft->zAlias, 

                             pRightTab, pRight->zAlias,

                             pRight->iCursor, &p->pWhere, isOuter);

       }

     }

   }

   return 0;

 }

 /*

 ** Insert code into "v" that will push the record on the top of the

 ** stack into the sorter.

 */

 static void pushOntoSorter(

   Parse *pParse,         /* Parser context */

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

   Select *pSelect,       /* The whole SELECT statement */

   int regData            /* Register holding data to be sorted */

 ){

   Vdbe *v = pParse->pVdbe;

   int nExpr = pOrderBy->nExpr;

   int regBase = sqlite3GetTempRange(pParse, nExpr+2);

   int regRecord = sqlite3GetTempReg(pParse);

   sqlite3ExprCodeExprList(pParse, pOrderBy, regBase, 0);

   sqlite3VdbeAddOp2(v, OP_Sequence, pOrderBy->iECursor, regBase+nExpr);

   sqlite3ExprCodeMove(pParse, regData, regBase+nExpr+1, 1);

   sqlite3VdbeAddOp3(v, OP_MakeRecord, regBase, nExpr + 2, regRecord);

   sqlite3VdbeAddOp2(v, OP_IdxInsert, pOrderBy->iECursor, regRecord);

   sqlite3ReleaseTempReg(pParse, regRecord);

   sqlite3ReleaseTempRange(pParse, regBase, nExpr+2);

   if( pSelect->iLimit ){

     int addr1, addr2;

     int iLimit;

     if( pSelect->iOffset ){

       iLimit = pSelect->iOffset+1;

     }else{

       iLimit = pSelect->iLimit;

     }

     addr1 = sqlite3VdbeAddOp1(v, OP_IfZero, iLimit);

     sqlite3VdbeAddOp2(v, OP_AddImm, iLimit, -1);

     addr2 = sqlite3VdbeAddOp0(v, OP_Goto);

     sqlite3VdbeJumpHere(v, addr1);

     sqlite3VdbeAddOp1(v, OP_Last, pOrderBy->iECursor);

     sqlite3VdbeAddOp1(v, OP_Delete, pOrderBy->iECursor);

     sqlite3VdbeJumpHere(v, addr2);

     pSelect->iLimit = 0;

   }

 }

 /*

 ** Add code to implement the OFFSET

 */

 static void codeOffset(

   Vdbe *v,          /* Generate code into this VM */

   Select *p,        /* The SELECT statement being coded */

   int iContinue     /* Jump here to skip the current record */

 ){

   if( p->iOffset && iContinue!=0 ){

     int addr;

     sqlite3VdbeAddOp2(v, OP_AddImm, p->iOffset, -1);

     addr = sqlite3VdbeAddOp1(v, OP_IfNeg, p->iOffset);

     sqlite3VdbeAddOp2(v, OP_Goto, 0, iContinue);

     VdbeComment((v, "skip OFFSET records"));

     sqlite3VdbeJumpHere(v, addr);

   }

 }

 /*

 ** Add code that will check to make sure the N registers starting at iMem

 ** form a distinct entry.  iTab is a sorting index that holds previously

 ** seen combinations of the N values.  A new entry is made in iTab

 ** if the current N values are new.

 **

 ** A jump to addrRepeat is made and the N+1 values are popped from the

 ** stack if the top N elements are not distinct.

 */

 static void codeDistinct(

   Parse *pParse,     /* Parsing and code generating context */

   int iTab,          /* A sorting index used to test for distinctness */

   int addrRepeat,    /* Jump to here if not distinct */

   int N,             /* Number of elements */

   int iMem           /* First element */

 ){

   Vdbe *v;

   int r1;

   v = pParse->pVdbe;

   r1 = sqlite3GetTempReg(pParse);

   sqlite3VdbeAddOp3(v, OP_MakeRecord, iMem, N, r1);

   sqlite3VdbeAddOp3(v, OP_Found, iTab, addrRepeat, r1);

   sqlite3VdbeAddOp2(v, OP_IdxInsert, iTab, r1);

   sqlite3ReleaseTempReg(pParse, r1);

 }

 /*

 ** Generate an error message when a SELECT is used within a subexpression

 ** (example:  "a IN (SELECT * FROM table)") but it has more than 1 result

 ** column.  We do this in a subroutine because the error occurs in multiple

 ** places.

 */

 static int checkForMultiColumnSelectError(

   Parse *pParse,       /* Parse context. */

   SelectDest *pDest,   /* Destination of SELECT results */

   int nExpr            /* Number of result columns returned by SELECT */

 ){

   int eDest = pDest->eDest;

   if( nExpr>1 && (eDest==SRT_Mem || eDest==SRT_Set) ){

     sqlite3ErrorMsg(pParse, "only a single result allowed for "

        "a SELECT that is part of an expression");

     return 1;

   }else{

     return 0;

   }

 }

 /*

 ** This routine generates the code for the inside of the inner loop

 ** of a SELECT.

 **

 ** If srcTab and nColumn are both zero, then the pEList expressions

 ** are evaluated in order to get the data for this row.  If nColumn>0

 ** then data is pulled from srcTab and pEList is used only to get the

 ** datatypes for each column.

 */

 static void selectInnerLoop(

   Parse *pParse,          /* The parser context */

   Select *p,              /* The complete select statement being coded */

   ExprList *pEList,       /* List of values being extracted */

   int srcTab,             /* Pull data from this table */

   int nColumn,            /* Number of columns in the source table */

   ExprList *pOrderBy,     /* If not NULL, sort results using this key */

   int distinct,           /* If >=0, make sure results are distinct */

   SelectDest *pDest,      /* How to dispose of the results */

   int iContinue,          /* Jump here to continue with next row */

   int iBreak              /* Jump here to break out of the inner loop */

 ){

   Vdbe *v = pParse->pVdbe;

   int i;

   int hasDistinct;        /* True if the DISTINCT keyword is present */

   int regResult;              /* Start of memory holding result set */

   int eDest = pDest->eDest;   /* How to dispose of results */

   int iParm = pDest->iParm;   /* First argument to disposal method */

   int nResultCol;             /* Number of result columns */

   if( v==0 ) return;

   assert( pEList!=0 );

   hasDistinct = distinct>=0;

   if( pOrderBy==0 && !hasDistinct ){

     codeOffset(v, p, iContinue);

   }

   /* Pull the requested columns.

   */

   if( nColumn>0 ){

     nResultCol = nColumn;

   }else{

     nResultCol = pEList->nExpr;

   }

   if( pDest->iMem==0 ){

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

     pDest->nMem = nResultCol;

     pParse->nMem += nResultCol;

   }else if( pDest->nMem!=nResultCol ){

     /* This happens when two SELECTs of a compound SELECT have differing

     ** numbers of result columns.  The error message will be generated by

     ** a higher-level routine. */

     return;

   }

   regResult = pDest->iMem;

   if( nColumn>0 ){

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

       sqlite3VdbeAddOp3(v, OP_Column, srcTab, i, regResult+i);

     }

   }else if( eDest!=SRT_Exists ){

     /* If the destination is an EXISTS(...) expression, the actual

     ** values returned by the SELECT are not required.

     */

     sqlite3ExprCodeExprList(pParse, pEList, regResult, eDest==SRT_Output);

   }

   nColumn = nResultCol;

   /* If the DISTINCT keyword was present on the SELECT statement

   ** and this row has been seen before, then do not make this row

   ** part of the result.

   */

   if( hasDistinct ){

     assert( pEList!=0 );

     assert( pEList->nExpr==nColumn );

     codeDistinct(pParse, distinct, iContinue, nColumn, regResult);

     if( pOrderBy==0 ){

       codeOffset(v, p, iContinue);

     }

   }

   if( checkForMultiColumnSelectError(pParse, pDest, pEList->nExpr) ){

     return;

   }

   switch( eDest ){

     /* In this mode, write each query result to the key of the temporary

     ** table iParm.

     */

 #ifndef SQLITE_OMIT_COMPOUND_SELECT

     case SRT_Union: {

       int r1;

       r1 = sqlite3GetTempReg(pParse);

       sqlite3VdbeAddOp3(v, OP_MakeRecord, regResult, nColumn, r1);

       sqlite3VdbeAddOp2(v, OP_IdxInsert, iParm, r1);

       sqlite3ReleaseTempReg(pParse, r1);

       break;

     }

     /* Construct a record from the query result, but instead of

     ** saving that record, use it as a key to delete elements from

     ** the temporary table iParm.

     */

     case SRT_Except: {

       sqlite3VdbeAddOp3(v, OP_IdxDelete, iParm, regResult, nColumn);

       break;

     }

 #endif

     /* Store the result as data using a unique key.

     */

     case SRT_Table:

     case SRT_EphemTab: {

       int r1 = sqlite3GetTempReg(pParse);

       sqlite3VdbeAddOp3(v, OP_MakeRecord, regResult, nColumn, r1);

       if( pOrderBy ){

         pushOntoSorter(pParse, pOrderBy, p, r1);

       }else{

         int r2 = sqlite3GetTempReg(pParse);

         sqlite3VdbeAddOp2(v, OP_NewRowid, iParm, r2);

         sqlite3VdbeAddOp3(v, OP_Insert, iParm, r1, r2);

         sqlite3VdbeChangeP5(v, OPFLAG_APPEND);

         sqlite3ReleaseTempReg(pParse, r2);

       }

       sqlite3ReleaseTempReg(pParse, r1);

       break;

     }

 #ifndef SQLITE_OMIT_SUBQUERY

     /* If we are creating a set for an "expr IN (SELECT ...)" construct,

     ** then there should be a single item on the stack.  Write this

     ** item into the set table with bogus data.

     */

     case SRT_Set: {

       assert( nColumn==1 );

       p->affinity = sqlite3CompareAffinity(pEList->a[0].pExpr, pDest->affinity);

       if( pOrderBy ){

         /* At first glance you would think we could optimize out the

         ** ORDER BY in this case since the order of entries in the set

         ** does not matter.  But there might be a LIMIT clause, in which

         ** case the order does matter */

         pushOntoSorter(pParse, pOrderBy, p, regResult);

       }else{

         int r1 = sqlite3GetTempReg(pParse);

         sqlite3VdbeAddOp4(v, OP_MakeRecord, regResult, 1, r1, &p->affinity, 1);

         sqlite3ExprCacheAffinityChange(pParse, regResult, 1);

         sqlite3VdbeAddOp2(v, OP_IdxInsert, iParm, r1);

         sqlite3ReleaseTempReg(pParse, r1);

       }

       break;

     }

     /* If any row exist in the result set, record that fact and abort.

     */

     case SRT_Exists: {

       sqlite3VdbeAddOp2(v, OP_Integer, 1, iParm);

       /* The LIMIT clause will terminate the loop for us */

       break;

     }

     /* If this is a scalar select that is part of an expression, then

     ** store the results in the appropriate memory cell and break out

     ** of the scan loop.

     */

     case SRT_Mem: {

       assert( nColumn==1 );

       if( pOrderBy ){

         pushOntoSorter(pParse, pOrderBy, p, regResult);

       }else{

         sqlite3ExprCodeMove(pParse, regResult, iParm, 1);

         /* The LIMIT clause will jump out of the loop for us */

       }

       break;

     }

 #endif /* #ifndef SQLITE_OMIT_SUBQUERY */

     /* Send the data to the callback function or to a subroutine.  In the

     ** case of a subroutine, the subroutine itself is responsible for

     ** popping the data from the stack.

     */

     case SRT_Coroutine:

     case SRT_Output: {

       if( pOrderBy ){

         int r1 = sqlite3GetTempReg(pParse);

         sqlite3VdbeAddOp3(v, OP_MakeRecord, regResult, nColumn, r1);

         pushOntoSorter(pParse, pOrderBy, p, r1);

         sqlite3ReleaseTempReg(pParse, r1);

       }else if( eDest==SRT_Coroutine ){

         sqlite3VdbeAddOp1(v, OP_Yield, pDest->iParm);

       }else{

         sqlite3VdbeAddOp2(v, OP_ResultRow, regResult, nColumn);

         sqlite3ExprCacheAffinityChange(pParse, regResult, nColumn);

       }

       break;

     }

 #if !defined(SQLITE_OMIT_TRIGGER)

     /* Discard the results.  This is used for SELECT statements inside

     ** the body of a TRIGGER.  The purpose of such selects is to call

     ** user-defined functions that have side effects.  We do not care

     ** about the actual results of the select.

     */

     default: {

       assert( eDest==SRT_Discard );

       break;

     }

 #endif

   }

   /* Jump to the end of the loop if the LIMIT is reached.

   */

   if( p->iLimit ){

     assert( pOrderBy==0 );  /* If there is an ORDER BY, the call to

                             ** pushOntoSorter() would have cleared p->iLimit */

     sqlite3VdbeAddOp2(v, OP_AddImm, p->iLimit, -1);

     sqlite3VdbeAddOp2(v, OP_IfZero, p->iLimit, iBreak);

   }

 }

 /*

 ** Given an expression list, generate a KeyInfo structure that records

 ** the collating sequence for each expression in that expression list.

 **

 ** If the ExprList is an ORDER BY or GROUP BY clause then the resulting

 ** KeyInfo structure is appropriate for initializing a virtual index to

 ** implement that clause.  If the ExprList is the result set of a SELECT

 ** then the KeyInfo structure is appropriate for initializing a virtual

 ** index to implement a DISTINCT test.

 **

 ** Space to hold the KeyInfo structure is obtain from malloc.  The calling

 ** function is responsible for seeing that this structure is eventually

 ** freed.  Add the KeyInfo structure to the P4 field of an opcode using

 ** P4_KEYINFO_HANDOFF is the usual way of dealing with this.

 */

 static KeyInfo *keyInfoFromExprList(Parse *pParse, ExprList *pList){

   sqlite3 *db = pParse->db;

   int nExpr;

   KeyInfo *pInfo;

   struct ExprList_item *pItem;

   int i;

   nExpr = pList->nExpr;

   pInfo = sqlite3DbMallocZero(db, sizeof(*pInfo) + nExpr*(sizeof(CollSeq*)+1) );

   if( pInfo ){

     pInfo->aSortOrder = (u8*)&pInfo->aColl[nExpr];

     pInfo->nField = nExpr;

     pInfo->enc = ENC(db);

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

       CollSeq *pColl;

       pColl = sqlite3ExprCollSeq(pParse, pItem->pExpr);

       if( !pColl ){

         pColl = db->pDfltColl;

       }

       pInfo->aColl[i] = pColl;

       pInfo->aSortOrder[i] = pItem->sortOrder;

     }

   }

   return pInfo;

 }

 /*

 ** If the inner loop was generated using a non-null pOrderBy argument,

 ** then the results were placed in a sorter.  After the loop is terminated

 ** we need to run the sorter and output the results.  The following

 ** routine generates the code needed to do that.

 */

 static void generateSortTail(

   Parse *pParse,    /* Parsing context */

   Select *p,        /* The SELECT statement */

   Vdbe *v,          /* Generate code into this VDBE */

   int nColumn,      /* Number of columns of data */

   SelectDest *pDest /* Write the sorted results here */

 ){

   int brk = sqlite3VdbeMakeLabel(v);

   int cont = sqlite3VdbeMakeLabel(v);

   int addr;

   int iTab;

   int pseudoTab = 0;

   ExprList *pOrderBy = p->pOrderBy;

   int eDest = pDest->eDest;

   int iParm = pDest->iParm;

   int regRow;

   int regRowid;

   iTab = pOrderBy->iECursor;

   if( eDest==SRT_Output || eDest==SRT_Coroutine ){

     pseudoTab = pParse->nTab++;

     sqlite3VdbeAddOp2(v, OP_SetNumColumns, 0, nColumn);

     sqlite3VdbeAddOp2(v, OP_OpenPseudo, pseudoTab, eDest==SRT_Output);

   }

   addr = 1 + sqlite3VdbeAddOp2(v, OP_Sort, iTab, brk);

   codeOffset(v, p, cont);

   regRow = sqlite3GetTempReg(pParse);

   regRowid = sqlite3GetTempReg(pParse);

   sqlite3VdbeAddOp3(v, OP_Column, iTab, pOrderBy->nExpr + 1, regRow);

   switch( eDest ){

     case SRT_Table:

     case SRT_EphemTab: {

       sqlite3VdbeAddOp2(v, OP_NewRowid, iParm, regRowid);

       sqlite3VdbeAddOp3(v, OP_Insert, iParm, regRow, regRowid);

       sqlite3VdbeChangeP5(v, OPFLAG_APPEND);

       break;

     }

 #ifndef SQLITE_OMIT_SUBQUERY

     case SRT_Set: {

       assert( nColumn==1 );

       sqlite3VdbeAddOp4(v, OP_MakeRecord, regRow, 1, regRowid, &p->affinity, 1);

       sqlite3ExprCacheAffinityChange(pParse, regRow, 1);

       sqlite3VdbeAddOp2(v, OP_IdxInsert, iParm, regRowid);

       break;

     }

     case SRT_Mem: {

       assert( nColumn==1 );

       sqlite3ExprCodeMove(pParse, regRow, iParm, 1);

       /* The LIMIT clause will terminate the loop for us */

       break;

     }

 #endif

     case SRT_Output:

     case SRT_Coroutine: {

       int i;

       sqlite3VdbeAddOp2(v, OP_Integer, 1, regRowid);

       sqlite3VdbeAddOp3(v, OP_Insert, pseudoTab, regRow, regRowid);

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

         assert( regRow!=pDest->iMem+i );

         sqlite3VdbeAddOp3(v, OP_Column, pseudoTab, i, pDest->iMem+i);

       }

       if( eDest==SRT_Output ){

         sqlite3VdbeAddOp2(v, OP_ResultRow, pDest->iMem, nColumn);

         sqlite3ExprCacheAffinityChange(pParse, pDest->iMem, nColumn);

       }else{

         sqlite3VdbeAddOp1(v, OP_Yield, pDest->iParm);

       }

       break;

     }

     default: {

       /* Do nothing */

       break;

     }

   }

   sqlite3ReleaseTempReg(pParse, regRow);

   sqlite3ReleaseTempReg(pParse, regRowid);

   /* LIMIT has been implemented by the pushOntoSorter() routine.

   */

   assert( p->iLimit==0 );

   /* The bottom of the loop

   */

   sqlite3VdbeResolveLabel(v, cont);

   sqlite3VdbeAddOp2(v, OP_Next, iTab, addr);

   sqlite3VdbeResolveLabel(v, brk);

   if( eDest==SRT_Output || eDest==SRT_Coroutine ){

     sqlite3VdbeAddOp2(v, OP_Close, pseudoTab, 0);

   }

 }

 /*

 ** Return a pointer to a string containing the 'declaration type' of the

 ** expression pExpr. The string may be treated as static by the caller.

 **

 ** The declaration type is the exact datatype definition extracted from the

 ** original CREATE TABLE statement if the expression is a column. The

 ** declaration type for a ROWID field is INTEGER. Exactly when an expression

 ** is considered a column can be complex in the presence of subqueries. The

 ** result-set expression in all of the following SELECT statements is 

 ** considered a column by this function.

 **

 **   SELECT col FROM tbl;

 **   SELECT (SELECT col FROM tbl;

 **   SELECT (SELECT col FROM tbl);

 **   SELECT abc FROM (SELECT col AS abc FROM tbl);

 ** 

 ** The declaration type for any expression other than a column is NULL.

 */

 static const char *columnType(

   NameContext *pNC, 

   Expr *pExpr,

   const char **pzOriginDb,

   const char **pzOriginTab,

   const char **pzOriginCol

 ){

   char const *zType = 0;

   char const *zOriginDb = 0;

   char const *zOriginTab = 0;

   char const *zOriginCol = 0;

   int j;

   if( pExpr==0 || pNC->pSrcList==0 ) return 0;

   switch( pExpr->op ){

     case TK_AGG_COLUMN:

     case TK_COLUMN: {

       /* The expression is a column. Locate the table the column is being

       ** extracted from in NameContext.pSrcList. This table may be real

       ** database table or a subquery.

       */

       Table *pTab = 0;            /* Table structure column is extracted from */

       Select *pS = 0;             /* Select the column is extracted from */

       int iCol = pExpr->iColumn;  /* Index of column in pTab */

       while( pNC && !pTab ){

         SrcList *pTabList = pNC->pSrcList;

         for(j=0;j<pTabList->nSrc && pTabList->a[j].iCursor!=pExpr->iTable;j++);

         if( j<pTabList->nSrc ){

           pTab = pTabList->a[j].pTab;

           pS = pTabList->a[j].pSelect;

         }else{

           pNC = pNC->pNext;

         }

       }

       if( pTab==0 ){

         /* FIX ME:

         ** This can occurs if you have something like "SELECT new.x;" inside

         ** a trigger.  In other words, if you reference the special "new"

         ** table in the result set of a select.  We do not have a good way

         ** to find the actual table type, so call it "TEXT".  This is really

         ** something of a bug, but I do not know how to fix it.

         **

         ** This code does not produce the correct answer - it just prevents

         ** a segfault.  See ticket #1229.

         */

         zType = "TEXT";

         break;

       }

       assert( pTab );

       if( pS ){

         /* The "table" is actually a sub-select or a view in the FROM clause

         ** of the SELECT statement. Return the declaration type and origin

         ** data for the result-set column of the sub-select.

         */

         if( iCol>=0 && iCol<pS->pEList->nExpr ){

           /* If iCol is less than zero, then the expression requests the

           ** rowid of the sub-select or view. This expression is legal (see 

           ** test case misc2.2.2) - it always evaluates to NULL.

           */

           NameContext sNC;

           Expr *p = pS->pEList->a[iCol].pExpr;

           sNC.pSrcList = pS->pSrc;

           sNC.pNext = 0;

           sNC.pParse = pNC->pParse;

           zType = columnType(&sNC, p, &zOriginDb, &zOriginTab, &zOriginCol); 

         }

       }else if( pTab->pSchema ){

         /* A real table */

         assert( !pS );

         if( iCol<0 ) iCol = pTab->iPKey;

         assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );

         if( iCol<0 ){

           zType = "INTEGER";

           zOriginCol = "rowid";

         }else{

           zType = pTab->aCol[iCol].zType;

           zOriginCol = pTab->aCol[iCol].zName;

         }

         zOriginTab = pTab->zName;

         if( pNC->pParse ){

           int iDb = sqlite3SchemaToIndex(pNC->pParse->db, pTab->pSchema);

           zOriginDb = pNC->pParse->db->aDb[iDb].zName;

         }

       }

       break;

     }

 #ifndef SQLITE_OMIT_SUBQUERY

     case TK_SELECT: {

       /* The expression is a sub-select. Return the declaration type and

       ** origin info for the single column in the result set of the SELECT

       ** statement.

       */

       NameContext sNC;

       Select *pS = pExpr->pSelect;

       Expr *p = pS->pEList->a[0].pExpr;

       sNC.pSrcList = pS->pSrc;

       sNC.pNext = pNC;

       sNC.pParse = pNC->pParse;

       zType = columnType(&sNC, p, &zOriginDb, &zOriginTab, &zOriginCol); 

       break;

     }

 #endif

   }

   if( pzOriginDb ){

     assert( pzOriginTab && pzOriginCol );

     *pzOriginDb = zOriginDb;

     *pzOriginTab = zOriginTab;

     *pzOriginCol = zOriginCol;

   }

   return zType;

 }

 /*

 ** Generate code that will tell the VDBE the declaration types of columns

 ** in the result set.

 */

 static void generateColumnTypes(

   Parse *pParse,      /* Parser context */

   SrcList *pTabList,  /* List of tables */

   ExprList *pEList    /* Expressions defining the result set */

 ){

 #ifndef SQLITE_OMIT_DECLTYPE

   Vdbe *v = pParse->pVdbe;

   int i;

   NameContext sNC;

   sNC.pSrcList = pTabList;

   sNC.pParse = pParse;

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

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

     const char *zType;

 #ifdef SQLITE_ENABLE_COLUMN_METADATA

     const char *zOrigDb = 0;

     const char *zOrigTab = 0;

     const char *zOrigCol = 0;

     zType = columnType(&sNC, p, &zOrigDb, &zOrigTab, &zOrigCol);

     /* The vdbe must make its own copy of the column-type and other 

     ** column specific strings, in case the schema is reset before this

     ** virtual machine is deleted.

     */

     sqlite3VdbeSetColName(v, i, COLNAME_DATABASE, zOrigDb, P4_TRANSIENT);

     sqlite3VdbeSetColName(v, i, COLNAME_TABLE, zOrigTab, P4_TRANSIENT);

     sqlite3VdbeSetColName(v, i, COLNAME_COLUMN, zOrigCol, P4_TRANSIENT);

 #else

     zType = columnType(&sNC, p, 0, 0, 0);

 #endif

     sqlite3VdbeSetColName(v, i, COLNAME_DECLTYPE, zType, P4_TRANSIENT);

   }

 #endif /* SQLITE_OMIT_DECLTYPE */

 }

 /*

 ** Generate code that will tell the VDBE the names of columns

 ** in the result set.  This information is used to provide the

 ** azCol[] values in the callback.

 */

 static void generateColumnNames(

   Parse *pParse,      /* Parser context */

   SrcList *pTabList,  /* List of tables */

   ExprList *pEList    /* Expressions defining the result set */

 ){

   Vdbe *v = pParse->pVdbe;

   int i, j;

   sqlite3 *db = pParse->db;

   int fullNames, shortNames;

 #ifndef SQLITE_OMIT_EXPLAIN

   /* If this is an EXPLAIN, skip this step */

   if( pParse->explain ){

     return;

   }

 #endif

   assert( v!=0 );

   if( pParse->colNamesSet || v==0 || db->mallocFailed ) return;

   pParse->colNamesSet = 1;

   fullNames = (db->flags & SQLITE_FullColNames)!=0;

   shortNames = (db->flags & SQLITE_ShortColNames)!=0;

   sqlite3VdbeSetNumCols(v, pEList->nExpr);

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

     Expr *p;

     p = pEList->a[i].pExpr;

     if( p==0 ) continue;

     if( pEList->a[i].zName ){

       char *zName = pEList->a[i].zName;

       sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, strlen(zName));

     }else if( (p->op==TK_COLUMN || p->op==TK_AGG_COLUMN) && pTabList ){

       Table *pTab;

       char *zCol;

       int iCol = p->iColumn;

       for(j=0; j<pTabList->nSrc && pTabList->a[j].iCursor!=p->iTable; j++){}

       assert( j<pTabList->nSrc );

       pTab = pTabList->a[j].pTab;

       if( iCol<0 ) iCol = pTab->iPKey;

       assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );

       if( iCol<0 ){

         zCol = "rowid";

       }else{

         zCol = pTab->aCol[iCol].zName;

       }

       if( !shortNames && !fullNames ){

         sqlite3VdbeSetColName(v, i, COLNAME_NAME, (char*)p->span.z, p->span.n);

       }else if( fullNames || (!shortNames && pTabList->nSrc>1) ){

         char *zName = 0;

         char *zTab;

         zTab = pTabList->a[j].zAlias;

         if( fullNames || zTab==0 ) zTab = pTab->zName;

         zName = sqlite3MPrintf(db, "%s.%s", zTab, zCol);

         sqlite3VdbeSetColName(v, i, COLNAME_NAME, zName, P4_DYNAMIC);

       }else{

         sqlite3VdbeSetColName(v, i, COLNAME_NAME, zCol, strlen(zCol));

       }

     }else{

       sqlite3VdbeSetColName(v, i, COLNAME_NAME, (char*)p->span.z, p->span.n);

     }

   }

   generateColumnTypes(pParse, pTabList, pEList);

 }

 #ifndef SQLITE_OMIT_COMPOUND_SELECT

 /*

 ** Name of the connection operator, used for error messages.

 */

 static const char *selectOpName(int id){

   char *z;

   switch( id ){

     case TK_ALL:       z = "UNION ALL";   break;

     case TK_INTERSECT: z = "INTERSECT";   break;

     case TK_EXCEPT:    z = "EXCEPT";      break;

     default:           z = "UNION";       break;

   }

   return z;

 }

 #endif /* SQLITE_OMIT_COMPOUND_SELECT */

 /*

 ** Given a an expression list (which is really the list of expressions

 ** that form the result set of a SELECT statement) compute appropriate

 ** column names for a table that would hold the expression list.

 **

 ** All column names will be unique.

 **

 ** Only the column names are computed.  Column.zType, Column.zColl,

 ** and other fields of Column are zeroed.

 **

 ** Return SQLITE_OK on success.  If a memory allocation error occurs,

 ** store NULL in *paCol and 0 in *pnCol and return SQLITE_NOMEM.

 */

 static int selectColumnsFromExprList(

   Parse *pParse,          /* Parsing context */

   ExprList *pEList,       /* Expr list from which to derive column names */

   int *pnCol,             /* Write the number of columns here */

   Column **paCol          /* Write the new column list here */

 ){

   sqlite3 *db = pParse->db;

   int i, j, cnt;

   Column *aCol, *pCol;

   int nCol;

   Expr *p;

   char *zName;

   int nName;

   *pnCol = nCol = pEList->nExpr;

   aCol = *paCol = sqlite3DbMallocZero(db, sizeof(aCol[0])*nCol);

   if( aCol==0 ) return SQLITE_NOMEM;

   for(i=0, pCol=aCol; i<nCol; i++, pCol++){

     /* Get an appropriate name for the column

     */

     p = pEList->a[i].pExpr;

     assert( p->pRight==0 || p->pRight->token.z==0 || p->pRight->token.z[0]!=0 );

     if( (zName = pEList->a[i].zName)!=0 ){

       /* If the column contains an "AS <name>" phrase, use <name> as the name */

       zName = sqlite3DbStrDup(db, zName);

     }else{

       Expr *pCol = p;

       Table *pTab;

       while( pCol->op==TK_DOT ) pCol = pCol->pRight;

       if( pCol->op==TK_COLUMN && (pTab = pCol->pTab)!=0 ){

         /* For columns use the column name name */

         int iCol = pCol->iColumn;

         if( iCol<0 ) iCol = pTab->iPKey;

         zName = sqlite3MPrintf(db, "%s",

                  iCol>=0 ? pTab->aCol[iCol].zName : "rowid");

       }else{

         /* Use the original text of the column expression as its name */

         Token *pToken = (pCol->span.z?&pCol->span:&pCol->token);

         zName = sqlite3MPrintf(db, "%T", pToken);

       }

     }

     if( db->mallocFailed ){

       sqlite3DbFree(db, zName);

       break;

     }

     sqlite3Dequote(zName);

     /* Make sure the column name is unique.  If the name is not unique,

     ** append a integer to the name so that it becomes unique.

     */

     nName = strlen(zName);

     for(j=cnt=0; j<i; j++){

       if( sqlite3StrICmp(aCol[j].zName, zName)==0 ){

         char *zNewName;

         zName[nName] = 0;

         zNewName = sqlite3MPrintf(db, "%s:%d", zName, ++cnt);

         sqlite3DbFree(db, zName);

         zName = zNewName;

         j = -1;

         if( zName==0 ) break;

       }

     }

     pCol->zName = zName;

   }

   if( db->mallocFailed ){

     int j;

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

       sqlite3DbFree(db, aCol[j].zName);

     }

     sqlite3DbFree(db, aCol);

     *paCol = 0;

     *pnCol = 0;

     return SQLITE_NOMEM;

   }

   return SQLITE_OK;

 }

 /*

 ** Add type and collation information to a column list based on

 ** a SELECT statement.

 ** 

 ** The column list presumably came from selectColumnNamesFromExprList().

 ** The column list has only names, not types or collations.  This

 ** routine goes through and adds the types and collations.

 **

 ** This routine requires that all indentifiers in the SELECT

 ** statement be resolved.

 */

 static void selectAddColumnTypeAndCollation(

   Parse *pParse,        /* Parsing contexts */

   int nCol,             /* Number of columns */

   Column *aCol,         /* List of columns */

   Select *pSelect       /* SELECT used to determine types and collations */

 ){

   sqlite3 *db = pParse->db;

   NameContext sNC;

   Column *pCol;

   CollSeq *pColl;

   int i;

   Expr *p;

   struct ExprList_item *a;

   assert( pSelect!=0 );

   assert( (pSelect->selFlags & SF_Resolved)!=0 );

   assert( nCol==pSelect->pEList->nExpr || db->mallocFailed );

   if( db->mallocFailed ) return;

   memset(&sNC, 0, sizeof(sNC));

   sNC.pSrcList = pSelect->pSrc;

   a = pSelect->pEList->a;

   for(i=0, pCol=aCol; i<nCol; i++, pCol++){

     p = a[i].pExpr;

     pCol->zType = sqlite3DbStrDup(db, columnType(&sNC, p, 0, 0, 0));

     pCol->affinity = sqlite3ExprAffinity(p);

     pColl = sqlite3ExprCollSeq(pParse, p);

     if( pColl ){

       pCol->zColl = sqlite3DbStrDup(db, pColl->zName);

     }

   }

 }

 /*

 ** Given a SELECT statement, generate a Table structure that describes

 ** the result set of that SELECT.

 */

 Table *sqlite3ResultSetOfSelect(Parse *pParse, Select *pSelect){

   Table *pTab;

   sqlite3 *db = pParse->db;

   int savedFlags;

   savedFlags = db->flags;

   db->flags &= ~SQLITE_FullColNames;

   db->flags |= SQLITE_ShortColNames;

   sqlite3SelectPrep(pParse, pSelect, 0);

   if( pParse->nErr ) return 0;

   while( pSelect->pPrior ) pSelect = pSelect->pPrior;

   db->flags = savedFlags;

   pTab = sqlite3DbMallocZero(db, sizeof(Table) );

   if( pTab==0 ){

     return 0;

   }

   pTab->db = db;

   pTab->nRef = 1;

   pTab->zName = 0;

   selectColumnsFromExprList(pParse, pSelect->pEList, &pTab->nCol, &pTab->aCol);

   selectAddColumnTypeAndCollation(pParse, pTab->nCol, pTab->aCol, pSelect);

   pTab->iPKey = -1;

   if( db->mallocFailed ){

     sqlite3DeleteTable(pTab);

     return 0;

   }

   return pTab;

 }

 /*

 ** Get a VDBE for the given parser context.  Create a new one if necessary.

 ** If an error occurs, return NULL and leave a message in pParse.

 */

 Vdbe *sqlite3GetVdbe(Parse *pParse){

   Vdbe *v = pParse->pVdbe;

   if( v==0 ){

     v = pParse->pVdbe = sqlite3VdbeCreate(pParse->db);

 #ifndef SQLITE_OMIT_TRACE

     if( v ){

       sqlite3VdbeAddOp0(v, OP_Trace);

     }

 #endif

   }

   return v;

 }

 /*

 ** Compute the iLimit and iOffset fields of the SELECT based on the

 ** pLimit and pOffset expressions.  pLimit and pOffset hold the expressions

 ** that appear in the original SQL statement after the LIMIT and OFFSET

 ** keywords.  Or NULL if those keywords are omitted. iLimit and iOffset 

 ** are the integer memory register numbers for counters used to compute 

 ** the limit and offset.  If there is no limit and/or offset, then 

 ** iLimit and iOffset are negative.

 **

 ** This routine changes the values of iLimit and iOffset only if

 ** a limit or offset is defined by pLimit and pOffset.  iLimit and

 ** iOffset should have been preset to appropriate default values

 ** (usually but not always -1) prior to calling this routine.

 ** Only if pLimit!=0 or pOffset!=0 do the limit registers get

 ** redefined.  The UNION ALL operator uses this property to force

 ** the reuse of the same limit and offset registers across multiple

 ** SELECT statements.

 */

 static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){

   Vdbe *v = 0;

   int iLimit = 0;

   int iOffset;

   int addr1;

   if( p->iLimit ) return;

   /* 

   ** "LIMIT -1" always shows all rows.  There is some

   ** contraversy about what the correct behavior should be.

   ** The current implementation interprets "LIMIT 0" to mean

   ** no rows.

   */

   if( p->pLimit ){

     p->iLimit = iLimit = ++pParse->nMem;

     v = sqlite3GetVdbe(pParse);

     if( v==0 ) return;

     sqlite3ExprCode(pParse, p->pLimit, iLimit);

     sqlite3VdbeAddOp1(v, OP_MustBeInt, iLimit);

     VdbeComment((v, "LIMIT counter"));

     sqlite3VdbeAddOp2(v, OP_IfZero, iLimit, iBreak);

   }

   if( p->pOffset ){

     p->iOffset = iOffset = ++pParse->nMem;

     if( p->pLimit ){

       pParse->nMem++;   /* Allocate an extra register for limit+offset */

     }

     v = sqlite3GetVdbe(pParse);

     if( v==0 ) return;

     sqlite3ExprCode(pParse, p->pOffset, iOffset);

     sqlite3VdbeAddOp1(v, OP_MustBeInt, iOffset);

     VdbeComment((v, "OFFSET counter"));

     addr1 = sqlite3VdbeAddOp1(v, OP_IfPos, iOffset);

     sqlite3VdbeAddOp2(v, OP_Integer, 0, iOffset);

     sqlite3VdbeJumpHere(v, addr1);

     if( p->pLimit ){

       sqlite3VdbeAddOp3(v, OP_Add, iLimit, iOffset, iOffset+1);

       VdbeComment((v, "LIMIT+OFFSET"));

       addr1 = sqlite3VdbeAddOp1(v, OP_IfPos, iLimit);

       sqlite3VdbeAddOp2(v, OP_Integer, -1, iOffset+1);

       sqlite3VdbeJumpHere(v, addr1);

     }

   }

 }

 #ifndef SQLITE_OMIT_COMPOUND_SELECT

 /*

 ** Return the appropriate collating sequence for the iCol-th column of

 ** the result set for the compound-select statement "p".  Return NULL if

 ** the column has no default collating sequence.

 **

 ** The collating sequence for the compound select is taken from the

 ** left-most term of the select that has a collating sequence.

 */

 static CollSeq *multiSelectCollSeq(Parse *pParse, Select *p, int iCol){

   CollSeq *pRet;

   if( p->pPrior ){

     pRet = multiSelectCollSeq(pParse, p->pPrior, iCol);

   }else{

     pRet = 0;

   }

   if( pRet==0 ){

     pRet = sqlite3ExprCollSeq(pParse, p->pEList->a[iCol].pExpr);

   }

   return pRet;

 }

 #endif /* SQLITE_OMIT_COMPOUND_SELECT */

 /* Forward reference */

 static int multiSelectOrderBy(

   Parse *pParse,        /* Parsing context */

   Select *p,            /* The right-most of SELECTs to be coded */

   SelectDest *pDest     /* What to do with query results */

 );

 #ifndef SQLITE_OMIT_COMPOUND_SELECT

 /*

 ** This routine is called to process a compound query form from

 ** two or more separate queries using UNION, UNION ALL, EXCEPT, or

 ** INTERSECT

 **

 ** "p" points to the right-most of the two queries.  the query on the

 ** left is p->pPrior.  The left query could also be a compound query

 ** in which case this routine will be called recursively. 

 **

 ** The results of the total query are to be written into a destination

 ** of type eDest with parameter iParm.

 **

 ** Example 1:  Consider a three-way compound SQL statement.

 **

 **     SELECT a FROM t1 UNION SELECT b FROM t2 UNION SELECT c FROM t3

 **

 ** This statement is parsed up as follows:

 **

 **     SELECT c FROM t3

 **      |

 **      `----->  SELECT b FROM t2

 **                |

 **                `------>  SELECT a FROM t1

 **

 ** The arrows in the diagram above represent the Select.pPrior pointer.

 ** So if this routine is called with p equal to the t3 query, then

 ** pPrior will be the t2 query.  p->op will be TK_UNION in this case.

 **

 ** Notice that because of the way SQLite parses compound SELECTs, the

 ** individual selects always group from left to right.

 */

 static int multiSelect(

   Parse *pParse,        /* Parsing context */

   Select *p,            /* The right-most of SELECTs to be coded */

   SelectDest *pDest     /* What to do with query results */

 ){

   int rc = SQLITE_OK;   /* Success code from a subroutine */

   Select *pPrior;       /* Another SELECT immediately to our left */

   Vdbe *v;              /* Generate code to this VDBE */

   SelectDest dest;      /* Alternative data destination */

   Select *pDelete = 0;  /* Chain of simple selects to delete */

   sqlite3 *db;          /* Database connection */

   /* Make sure there is no ORDER BY or LIMIT clause on prior SELECTs.  Only

   ** the last (right-most) SELECT in the series may have an ORDER BY or LIMIT.

   */

   assert( p && p->pPrior );  /* Calling function guarantees this much */

   db = pParse->db;

   pPrior = p->pPrior;

   assert( pPrior->pRightmost!=pPrior );

   assert( pPrior->pRightmost==p->pRightmost );

   dest = *pDest;

   if( pPrior->pOrderBy ){

     sqlite3ErrorMsg(pParse,"ORDER BY clause should come after %s not before",

       selectOpName(p->op));

     rc = 1;

     goto multi_select_end;

   }

   if( pPrior->pLimit ){

     sqlite3ErrorMsg(pParse,"LIMIT clause should come after %s not before",

       selectOpName(p->op));

     rc = 1;

     goto multi_select_end;

   }

   v = sqlite3GetVdbe(pParse);

   assert( v!=0 );  /* The VDBE already created by calling function */

   /* Create the destination temporary table if necessary

   */

   if( dest.eDest==SRT_EphemTab ){

     assert( p->pEList );

     sqlite3VdbeAddOp2(v, OP_OpenEphemeral, dest.iParm, p->pEList->nExpr);

     dest.eDest = SRT_Table;

   }

   /* Make sure all SELECTs in the statement have the same number of elements

   ** in their result sets.

   */

   assert( p->pEList && pPrior->pEList );

   if( p->pEList->nExpr!=pPrior->pEList->nExpr ){

     sqlite3ErrorMsg(pParse, "SELECTs to the left and right of %s"

       " do not have the same number of result columns", selectOpName(p->op));

     rc = 1;

     goto multi_select_end;

   }

   /* Compound SELECTs that have an ORDER BY clause are handled separately.

   */

   if( p->pOrderBy ){

     return multiSelectOrderBy(pParse, p, pDest);

   }

   /* Generate code for the left and right SELECT statements.

   */

   switch( p->op ){

     case TK_ALL: {

       int addr = 0;

       assert( !pPrior->pLimit );

       pPrior->pLimit = p->pLimit;

       pPrior->pOffset = p->pOffset;

       rc = sqlite3Select(pParse, pPrior, &dest);

       p->pLimit = 0;

       p->pOffset = 0;

       if( rc ){

         goto multi_select_end;

       }

       p->pPrior = 0;

       p->iLimit = pPrior->iLimit;

       p->iOffset = pPrior->iOffset;

       if( p->iLimit ){

         addr = sqlite3VdbeAddOp1(v, OP_IfZero, p->iLimit);

         VdbeComment((v, "Jump ahead if LIMIT reached"));

       }

       rc = sqlite3Select(pParse, p, &dest);

       pDelete = p->pPrior;

       p->pPrior = pPrior;

       if( rc ){

         goto multi_select_end;

       }

       if( addr ){

         sqlite3VdbeJumpHere(v, addr);

       }

       break;

     }

     case TK_EXCEPT:

     case TK_UNION: {

       int unionTab;    /* Cursor number of the temporary table holding result */

       int op = 0;      /* One of the SRT_ operations to apply to self */

       int priorOp;     /* The SRT_ operation to apply to prior selects */

       Expr *pLimit, *pOffset; /* Saved values of p->nLimit and p->nOffset */

       int addr;

       SelectDest uniondest;

       priorOp = SRT_Union;

       if( dest.eDest==priorOp && !p->pLimit && !p->pOffset ){

         /* We can reuse a temporary table generated by a SELECT to our

         ** right.

         */

         unionTab = dest.iParm;

       }else{

         /* We will need to create our own temporary table to hold the

         ** intermediate results.

         */

         unionTab = pParse->nTab++;

         assert( p->pOrderBy==0 );

         addr = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, unionTab, 0);

         assert( p->addrOpenEphm[0] == -1 );

         p->addrOpenEphm[0] = addr;

         p->pRightmost->selFlags |= SF_UsesEphemeral;

         assert( p->pEList );

       }

       /* Code the SELECT statements to our left

       */

       assert( !pPrior->pOrderBy );

       sqlite3SelectDestInit(&uniondest, priorOp, unionTab);

       rc = sqlite3Select(pParse, pPrior, &uniondest);

       if( rc ){

         goto multi_select_end;

       }

       /* Code the current SELECT statement

       */

       if( p->op==TK_EXCEPT ){

         op = SRT_Except;

       }else{

         assert( p->op==TK_UNION );

         op = SRT_Union;

       }

       p->pPrior = 0;

       pLimit = p->pLimit;

       p->pLimit = 0;

       pOffset = p->pOffset;

       p->pOffset = 0;

       uniondest.eDest = op;

       rc = sqlite3Select(pParse, p, &uniondest);

       /* Query flattening in sqlite3Select() might refill p->pOrderBy.

       ** Be sure to delete p->pOrderBy, therefore, to avoid a memory leak. */

       sqlite3ExprListDelete(db, p->pOrderBy);

       pDelete = p->pPrior;

       p->pPrior = pPrior;

       p->pOrderBy = 0;

       sqlite3ExprDelete(db, p->pLimit);

       p->pLimit = pLimit;

       p->pOffset = pOffset;

       p->iLimit = 0;

       p->iOffset = 0;

       if( rc ){

         goto multi_select_end;

       }

       /* Convert the data in the temporary table into whatever form

       ** it is that we currently need.

       */      

       if( dest.eDest!=priorOp || unionTab!=dest.iParm ){

         int iCont, iBreak, iStart;

         assert( p->pEList );

         if( dest.eDest==SRT_Output ){

           Select *pFirst = p;

           while( pFirst->pPrior ) pFirst = pFirst->pPrior;

           generateColumnNames(pParse, 0, pFirst->pEList);

         }

         iBreak = sqlite3VdbeMakeLabel(v);

         iCont = sqlite3VdbeMakeLabel(v);

         computeLimitRegisters(pParse, p, iBreak);

         sqlite3VdbeAddOp2(v, OP_Rewind, unionTab, iBreak);

         iStart = sqlite3VdbeCurrentAddr(v);

         selectInnerLoop(pParse, p, p->pEList, unionTab, p->pEList->nExpr,

                         0, -1, &dest, iCont, iBreak);

         sqlite3VdbeResolveLabel(v, iCont);

         sqlite3VdbeAddOp2(v, OP_Next, unionTab, iStart);

         sqlite3VdbeResolveLabel(v, iBreak);

         sqlite3VdbeAddOp2(v, OP_Close, unionTab, 0);

       }

       break;

     }

     case TK_INTERSECT: {

       int tab1, tab2;

       int iCont, iBreak, iStart;

       Expr *pLimit, *pOffset;

       int addr;

       SelectDest intersectdest;

       int r1;

       /* INTERSECT is different from the others since it requires

       ** two temporary tables.  Hence it has its own case.  Begin

       ** by allocating the tables we will need.

       */

       tab1 = pParse->nTab++;

       tab2 = pParse->nTab++;

       assert( p->pOrderBy==0 );

       addr = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, tab1, 0);

       assert( p->addrOpenEphm[0] == -1 );

       p->addrOpenEphm[0] = addr;

       p->pRightmost->selFlags |= SF_UsesEphemeral;

       assert( p->pEList );

       /* Code the SELECTs to our left into temporary table "tab1".

       */

       sqlite3SelectDestInit(&intersectdest, SRT_Union, tab1);

       rc = sqlite3Select(pParse, pPrior, &intersectdest);

       if( rc ){

         goto multi_select_end;

       }

       /* Code the current SELECT into temporary table "tab2"

       */

       addr = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, tab2, 0);

       assert( p->addrOpenEphm[1] == -1 );

       p->addrOpenEphm[1] = addr;

       p->pPrior = 0;

       pLimit = p->pLimit;

       p->pLimit = 0;

       pOffset = p->pOffset;

       p->pOffset = 0;

       intersectdest.iParm = tab2;

       rc = sqlite3Select(pParse, p, &intersectdest);

       pDelete = p->pPrior;

       p->pPrior = pPrior;

       sqlite3ExprDelete(db, p->pLimit);

       p->pLimit = pLimit;

       p->pOffset = pOffset;

       if( rc ){

         goto multi_select_end;

       }

       /* Generate code to take the intersection of the two temporary

       ** tables.

       */

       assert( p->pEList );

       if( dest.eDest==SRT_Output ){

         Select *pFirst = p;

         while( pFirst->pPrior ) pFirst = pFirst->pPrior;

         generateColumnNames(pParse, 0, pFirst->pEList);

       }

       iBreak = sqlite3VdbeMakeLabel(v);

       iCont = sqlite3VdbeMakeLabel(v);

       computeLimitRegisters(pParse, p, iBreak);

       sqlite3VdbeAddOp2(v, OP_Rewind, tab1, iBreak);

       r1 = sqlite3GetTempReg(pParse);

       iStart = sqlite3VdbeAddOp2(v, OP_RowKey, tab1, r1);

       sqlite3VdbeAddOp3(v, OP_NotFound, tab2, iCont, r1);

       sqlite3ReleaseTempReg(pParse, r1);

       selectInnerLoop(pParse, p, p->pEList, tab1, p->pEList->nExpr,

                       0, -1, &dest, iCont, iBreak);

       sqlite3VdbeResolveLabel(v, iCont);

       sqlite3VdbeAddOp2(v, OP_Next, tab1, iStart);

       sqlite3VdbeResolveLabel(v, iBreak);

       sqlite3VdbeAddOp2(v, OP_Close, tab2, 0);

       sqlite3VdbeAddOp2(v, OP_Close, tab1, 0);

       break;

     }

   }

   /* Compute collating sequences used by 

   ** temporary tables needed to implement the compound select.

   ** Attach the KeyInfo structure to all temporary tables.

   **

   ** This section is run by the right-most SELECT statement only.

   ** SELECT statements to the left always skip this part.  The right-most

   ** SELECT might also skip this part if it has no ORDER BY clause and

   ** no temp tables are required.

   */

   if( p->selFlags & SF_UsesEphemeral ){

     int i;                        /* Loop counter */

     KeyInfo *pKeyInfo;            /* Collating sequence for the result set */

     Select *pLoop;                /* For looping through SELECT statements */

     CollSeq **apColl;             /* For looping through pKeyInfo->aColl[] */

     int nCol;                     /* Number of columns in result set */

     assert( p->pRightmost==p );

     nCol = p->pEList->nExpr;

     pKeyInfo = sqlite3DbMallocZero(db,

                        sizeof(*pKeyInfo)+nCol*(sizeof(CollSeq*) + 1));

     if( !pKeyInfo ){

       rc = SQLITE_NOMEM;

       goto multi_select_end;

     }

     pKeyInfo->enc = ENC(db);

     pKeyInfo->nField = nCol;

     for(i=0, apColl=pKeyInfo->aColl; i<nCol; i++, apColl++){

       *apColl = multiSelectCollSeq(pParse, p, i);

       if( 0==*apColl ){

         *apColl = db->pDfltColl;

       }

     }

     for(pLoop=p; pLoop; pLoop=pLoop->pPrior){

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

         int addr = pLoop->addrOpenEphm[i];

         if( addr<0 ){

           /* If [0] is unused then [1] is also unused.  So we can

           ** always safely abort as soon as the first unused slot is found */

           assert( pLoop->addrOpenEphm[1]<0 );

           break;

         }

         sqlite3VdbeChangeP2(v, addr, nCol);

         sqlite3VdbeChangeP4(v, addr, (char*)pKeyInfo, P4_KEYINFO);

         pLoop->addrOpenEphm[i] = -1;

       }

     }

     sqlite3DbFree(db, pKeyInfo);

   }

 multi_select_end:

   pDest->iMem = dest.iMem;

   pDest->nMem = dest.nMem;

   sqlite3SelectDelete(db, pDelete);

   return rc;

 }

 #endif /* SQLITE_OMIT_COMPOUND_SELECT */

 /*

 ** Code an output subroutine for a coroutine implementation of a

 ** SELECT statment.

 **

 ** The data to be output is contained in pIn->iMem.  There are

 ** pIn->nMem columns to be output.  pDest is where the output should

 ** be sent.

 **

 ** regReturn is the number of the register holding the subroutine

 ** return address.

 **

 ** If regPrev>0 then it is a the first register in a vector that

 ** records the previous output.  mem[regPrev] is a flag that is false

 ** if there has been no previous output.  If regPrev>0 then code is

 ** generated to suppress duplicates.  pKeyInfo is used for comparing

 ** keys.

 **

 ** If the LIMIT found in p->iLimit is reached, jump immediately to

 ** iBreak.

 */

 static int generateOutputSubroutine(

   Parse *pParse,          /* Parsing context */

   Select *p,              /* The SELECT statement */

   SelectDest *pIn,        /* Coroutine supplying data */

   SelectDest *pDest,      /* Where to send the data */

   int regReturn,          /* The return address register */

   int regPrev,            /* Previous result register.  No uniqueness if 0 */

   KeyInfo *pKeyInfo,      /* For comparing with previous entry */

   int p4type,             /* The p4 type for pKeyInfo */

   int iBreak              /* Jump here if we hit the LIMIT */

 ){

   Vdbe *v = pParse->pVdbe;

   int iContinue;

   int addr;

   addr = sqlite3VdbeCurrentAddr(v);

   iContinue = sqlite3VdbeMakeLabel(v);

   /* Suppress duplicates for UNION, EXCEPT, and INTERSECT 

   */

   if( regPrev ){

     int j1, j2;

     j1 = sqlite3VdbeAddOp1(v, OP_IfNot, regPrev);

     j2 = sqlite3VdbeAddOp4(v, OP_Compare, pIn->iMem, regPrev+1, pIn->nMem,

                               (char*)pKeyInfo, p4type);

     sqlite3VdbeAddOp3(v, OP_Jump, j2+2, iContinue, j2+2);

     sqlite3VdbeJumpHere(v, j1);

     sqlite3ExprCodeCopy(pParse, pIn->iMem, regPrev+1, pIn->nMem);

     sqlite3VdbeAddOp2(v, OP_Integer, 1, regPrev);

   }

   if( pParse->db->mallocFailed ) return 0;

   /* Suppress the the first OFFSET entries if there is an OFFSET clause

   */

   codeOffset(v, p, iContinue);

   switch( pDest->eDest ){

     /* Store the result as data using a unique key.

     */

     case SRT_Table:

     case SRT_EphemTab: {

       int r1 = sqlite3GetTempReg(pParse);

       int r2 = sqlite3GetTempReg(pParse);

       sqlite3VdbeAddOp3(v, OP_MakeRecord, pIn->iMem, pIn->nMem, r1);

       sqlite3VdbeAddOp2(v, OP_NewRowid, pDest->iParm, r2);

       sqlite3VdbeAddOp3(v, OP_Insert, pDest->iParm, r1, r2);

       sqlite3VdbeChangeP5(v, OPFLAG_APPEND);

       sqlite3ReleaseTempReg(pParse, r2);

       sqlite3ReleaseTempReg(pParse, r1);

       break;

     }

 #ifndef SQLITE_OMIT_SUBQUERY

     /* If we are creating a set for an "expr IN (SELECT ...)" construct,

     ** then there should be a single item on the stack.  Write this

     ** item into the set table with bogus data.

     */

     case SRT_Set: {

       int r1;

       assert( pIn->nMem==1 );

       p->affinity = 

          sqlite3CompareAffinity(p->pEList->a[0].pExpr, pDest->affinity);

       r1 = sqlite3GetTempReg(pParse);

       sqlite3VdbeAddOp4(v, OP_MakeRecord, pIn->iMem, 1, r1, &p->affinity, 1);

       sqlite3ExprCacheAffinityChange(pParse, pIn->iMem, 1);

       sqlite3VdbeAddOp2(v, OP_IdxInsert, pDest->iParm, r1);

       sqlite3ReleaseTempReg(pParse, r1);

       break;

     }

 #if 0  /* Never occurs on an ORDER BY query */

     /* If any row exist in the result set, record that fact and abort.

     */

     case SRT_Exists: {

       sqlite3VdbeAddOp2(v, OP_Integer, 1, pDest->iParm);

       /* The LIMIT clause will terminate the loop for us */

       break;

     }

 #endif

     /* If this is a scalar select that is part of an expression, then

     ** store the results in the appropriate memory cell and break out

     ** of the scan loop.

     */

     case SRT_Mem: {

       assert( pIn->nMem==1 );

       sqlite3ExprCodeMove(pParse, pIn->iMem, pDest->iParm, 1);

       /* The LIMIT clause will jump out of the loop for us */

       break;

     }

 #endif /* #ifndef SQLITE_OMIT_SUBQUERY */

     /* The results are stored in a sequence of registers

     ** starting at pDest->iMem.  Then the co-routine yields.

     */

     case SRT_Coroutine: {

       if( pDest->iMem==0 ){

         pDest->iMem = sqlite3GetTempRange(pParse, pIn->nMem);

         pDest->nMem = pIn->nMem;

       }

       sqlite3ExprCodeMove(pParse, pIn->iMem, pDest->iMem, pDest->nMem);

       sqlite3VdbeAddOp1(v, OP_Yield, pDest->iParm);

       break;

     }

     /* Results are stored in a sequence of registers.  Then the

     ** OP_ResultRow opcode is used to cause sqlite3_step() to return

     ** the next row of result.

     */

     case SRT_Output: {

       sqlite3VdbeAddOp2(v, OP_ResultRow, pIn->iMem, pIn->nMem);

       sqlite3ExprCacheAffinityChange(pParse, pIn->iMem, pIn->nMem);

       break;

     }

 #if !defined(SQLITE_OMIT_TRIGGER)

     /* Discard the results.  This is used for SELECT statements inside

     ** the body of a TRIGGER.  The purpose of such selects is to call

     ** user-defined functions that have side effects.  We do not care

     ** about the actual results of the select.

     */

     default: {

       break;

     }

 #endif

   }

   /* Jump to the end of the loop if the LIMIT is reached.

   */

   if( p->iLimit ){

     sqlite3VdbeAddOp2(v, OP_AddImm, p->iLimit, -1);

     sqlite3VdbeAddOp2(v, OP_IfZero, p->iLimit, iBreak);

   }

   /* Generate the subroutine return

   */

   sqlite3VdbeResolveLabel(v, iContinue);

   sqlite3VdbeAddOp1(v, OP_Return, regReturn);

   return addr;

 }

 /*

 ** Alternative compound select code generator for cases when there

 ** is an ORDER BY clause.

 **

 ** We assume a query of the following form:

 **

 **      <selectA>  <operator>  <selectB>  ORDER BY <orderbylist>

 **

 ** <operator> is one of UNION ALL, UNION, EXCEPT, or INTERSECT.  The idea

 ** is to code both <selectA> and <selectB> with the ORDER BY clause as

 ** co-routines.  Then run the co-routines in parallel and merge the results

 ** into the output.  In addition to the two coroutines (called selectA and

 ** selectB) there are 7 subroutines:

 **

 **    outA:    Move the output of the selectA coroutine into the output

 **             of the compound query.

 **

 **    outB:    Move the output of the selectB coroutine into the output

 **             of the compound query.  (Only generated for UNION and

 **             UNION ALL.  EXCEPT and INSERTSECT never output a row that

 **             appears only in B.)

 **

 **    AltB:    Called when there is data from both coroutines and A<B.

 **

 **    AeqB:    Called when there is data from both coroutines and A==B.

 **

 **    AgtB:    Called when there is data from both coroutines and A>B.

 **

 **    EofA:    Called when data is exhausted from selectA.

 **

 **    EofB:    Called when data is exhausted from selectB.

 **

 ** The implementation of the latter five subroutines depend on which 

 ** <operator> is used:

 **

 **

 **             UNION ALL         UNION            EXCEPT          INTERSECT

 **          -------------  -----------------  --------------  -----------------

 **   AltB:   outA, nextA      outA, nextA       outA, nextA         nextA

 **

 **   AeqB:   outA, nextA         nextA             nextA         outA, nextA

 **

 **   AgtB:   outB, nextB      outB, nextB          nextB            nextB

 **

 **   EofA:   outB, nextB      outB, nextB          halt             halt

 **

 **   EofB:   outA, nextA      outA, nextA       outA, nextA         halt

 **

 ** In the AltB, AeqB, and AgtB subroutines, an EOF on A following nextA

 ** causes an immediate jump to EofA and an EOF on B following nextB causes

 ** an immediate jump to EofB.  Within EofA and EofB, and EOF on entry or

 ** following nextX causes a jump to the end of the select processing.

 **

 ** Duplicate removal in the UNION, EXCEPT, and INTERSECT cases is handled

 ** within the output subroutine.  The regPrev register set holds the previously

 ** output value.  A comparison is made against this value and the output

 ** is skipped if the next results would be the same as the previous.

 **

 ** The implementation plan is to implement the two coroutines and seven

 ** subroutines first, then put the control logic at the bottom.  Like this:

 **

 **          goto Init

 **     coA: coroutine for left query (A)

 **     coB: coroutine for right query (B)

 **    outA: output one row of A

 **    outB: output one row of B (UNION and UNION ALL only)

 **    EofA: ...

 **    EofB: ...

 **    AltB: ...

 **    AeqB: ...

 **    AgtB: ...

 **    Init: initialize coroutine registers

 **          yield coA

 **          if eof(A) goto EofA

 **          yield coB

 **          if eof(B) goto EofB

 **    Cmpr: Compare A, B

 **          Jump AltB, AeqB, AgtB

 **     End: ...

 **

 ** We call AltB, AeqB, AgtB, EofA, and EofB "subroutines" but they are not

 ** actually called using Gosub and they do not Return.  EofA and EofB loop

 ** until all data is exhausted then jump to the "end" labe.  AltB, AeqB,

 ** and AgtB jump to either L2 or to one of EofA or EofB.

 */

 #ifndef SQLITE_OMIT_COMPOUND_SELECT

 static int multiSelectOrderBy(

   Parse *pParse,        /* Parsing context */

   Select *p,            /* The right-most of SELECTs to be coded */

   SelectDest *pDest     /* What to do with query results */

 ){

   int i, j;             /* Loop counters */

   Select *pPrior;       /* Another SELECT immediately to our left */

   Vdbe *v;              /* Generate code to this VDBE */

   SelectDest destA;     /* Destination for coroutine A */

   SelectDest destB;     /* Destination for coroutine B */

   int regAddrA;         /* Address register for select-A coroutine */

   int regEofA;          /* Flag to indicate when select-A is complete */

   int regAddrB;         /* Address register for select-B coroutine */

   int regEofB;          /* Flag to indicate when select-B is complete */

   int addrSelectA;      /* Address of the select-A coroutine */

   int addrSelectB;      /* Address of the select-B coroutine */

   int regOutA;          /* Address register for the output-A subroutine */

   int regOutB;          /* Address register for the output-B subroutine */

   int addrOutA;         /* Address of the output-A subroutine */

   int addrOutB;         /* Address of the output-B subroutine */

   int addrEofA;         /* Address of the select-A-exhausted subroutine */

   int addrEofB;         /* Address of the select-B-exhausted subroutine */

   int addrAltB;         /* Address of the A<B subroutine */

   int addrAeqB;         /* Address of the A==B subroutine */

   int addrAgtB;         /* Address of the A>B subroutine */

   int regLimitA;        /* Limit register for select-A */

   int regLimitB;        /* Limit register for select-A */

   int regPrev;          /* A range of registers to hold previous output */

   int savedLimit;       /* Saved value of p->iLimit */

   int savedOffset;      /* Saved value of p->iOffset */

   int labelCmpr;        /* Label for the start of the merge algorithm */

   int labelEnd;         /* Label for the end of the overall SELECT stmt */

   int j1;               /* Jump instructions that get retargetted */

   int op;               /* One of TK_ALL, TK_UNION, TK_EXCEPT, TK_INTERSECT */

   KeyInfo *pKeyDup = 0; /* Comparison information for duplicate removal */

   KeyInfo *pKeyMerge;   /* Comparison information for merging rows */

   sqlite3 *db;          /* Database connection */

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

   int nOrderBy;         /* Number of terms in the ORDER BY clause */

   int *aPermute;        /* Mapping from ORDER BY terms to result set columns */

   assert( p->pOrderBy!=0 );

   assert( pKeyDup==0 ); /* "Managed" code needs this.  Ticket #3382. */

   db = pParse->db;

   v = pParse->pVdbe;

   if( v==0 ) return SQLITE_NOMEM;

   labelEnd = sqlite3VdbeMakeLabel(v);

   labelCmpr = sqlite3VdbeMakeLabel(v);

   /* Patch up the ORDER BY clause

   */

   op = p->op;  

   pPrior = p->pPrior;

   assert( pPrior->pOrderBy==0 );

   pOrderBy = p->pOrderBy;

   assert( pOrderBy );

   nOrderBy = pOrderBy->nExpr;

   /* For operators other than UNION ALL we have to make sure that

   ** the ORDER BY clause covers every term of the result set.  Add

   ** terms to the ORDER BY clause as necessary.

   */

   if( op!=TK_ALL ){

     for(i=1; db->mallocFailed==0 && i<=p->pEList->nExpr; i++){

       struct ExprList_item *pItem;

       for(j=0, pItem=pOrderBy->a; j<nOrderBy; j++, pItem++){

         assert( pItem->iCol>0 );

         if( pItem->iCol==i ) break;

       }

       if( j==nOrderBy ){

         Expr *pNew = sqlite3PExpr(pParse, TK_INTEGER, 0, 0, 0);

         if( pNew==0 ) return SQLITE_NOMEM;

         pNew->flags |= EP_IntValue;

         pNew->iTable = i;

         pOrderBy = sqlite3ExprListAppend(pParse, pOrderBy, pNew, 0);

         pOrderBy->a[nOrderBy++].iCol = i;

       }

     }

   }

   /* Compute the comparison permutation and keyinfo that is used with

   ** the permutation in order to comparisons to determine if the next

   ** row of results comes from selectA or selectB.  Also add explicit

   ** collations to the ORDER BY clause terms so that when the subqueries

   ** to the right and the left are evaluated, they use the correct

   ** collation.

   */

   aPermute = sqlite3DbMallocRaw(db, sizeof(int)*nOrderBy);

   if( aPermute ){

     struct ExprList_item *pItem;

     for(i=0, pItem=pOrderBy->a; i<nOrderBy; i++, pItem++){

       assert( pItem->iCol>0  && pItem->iCol<=p->pEList->nExpr );

       aPermute[i] = pItem->iCol - 1;

     }

     pKeyMerge =

       sqlite3DbMallocRaw(db, sizeof(*pKeyMerge)+nOrderBy*(sizeof(CollSeq*)+1));

     if( pKeyMerge ){

       pKeyMerge->aSortOrder = (u8*)&pKeyMerge->aColl[nOrderBy];

       pKeyMerge->nField = nOrderBy;

       pKeyMerge->enc = ENC(db);

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

         CollSeq *pColl;

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

         if( pTerm->flags & EP_ExpCollate ){

           pColl = pTerm->pColl;

         }else{

           pColl = multiSelectCollSeq(pParse, p, aPermute[i]);

           pTerm->flags |= EP_ExpCollate;

           pTerm->pColl = pColl;

         }

         pKeyMerge->aColl[i] = pColl;

         pKeyMerge->aSortOrder[i] = pOrderBy->a[i].sortOrder;

       }

     }

   }else{

     pKeyMerge = 0;

   }

   /* Reattach the ORDER BY clause to the query.

   */

   p->pOrderBy = pOrderBy;

   pPrior->pOrderBy = sqlite3ExprListDup(pParse->db, pOrderBy);

   /* Allocate a range of temporary registers and the KeyInfo needed

   ** for the logic that removes duplicate result rows when the

   ** operator is UNION, EXCEPT, or INTERSECT (but not UNION ALL).

   */

   if( op==TK_ALL ){

     regPrev = 0;

   }else{

     int nExpr = p->pEList->nExpr;

     assert( nOrderBy>=nExpr );

     regPrev = sqlite3GetTempRange(pParse, nExpr+1);

     sqlite3VdbeAddOp2(v, OP_Integer, 0, regPrev);

     pKeyDup = sqlite3DbMallocZero(db,

                   sizeof(*pKeyDup) + nExpr*(sizeof(CollSeq*)+1) );

     if( pKeyDup ){

       pKeyDup->aSortOrder = (u8*)&pKeyDup->aColl[nExpr];

       pKeyDup->nField = nExpr;

       pKeyDup->enc = ENC(db);

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

         pKeyDup->aColl[i] = multiSelectCollSeq(pParse, p, i);

         pKeyDup->aSortOrder[i] = 0;

       }

     }

   }

   /* Separate the left and the right query from one another

   */

   p->pPrior = 0;

   pPrior->pRightmost = 0;

   sqlite3ResolveOrderGroupBy(pParse, p, p->pOrderBy, "ORDER");

   if( pPrior->pPrior==0 ){

     sqlite3ResolveOrderGroupBy(pParse, pPrior, pPrior->pOrderBy, "ORDER");

   }

   /* Compute the limit registers */

   computeLimitRegisters(pParse, p, labelEnd);

   if( p->iLimit && op==TK_ALL ){

     regLimitA = ++pParse->nMem;

     regLimitB = ++pParse->nMem;

     sqlite3VdbeAddOp2(v, OP_Copy, p->iOffset ? p->iOffset+1 : p->iLimit,

                                   regLimitA);

     sqlite3VdbeAddOp2(v, OP_Copy, regLimitA, regLimitB);

   }else{

     regLimitA = regLimitB = 0;

   }

   sqlite3ExprDelete(db, p->pLimit);

   p->pLimit = 0;

   sqlite3ExprDelete(db, p->pOffset);

   p->pOffset = 0;

   regAddrA = ++pParse->nMem;

   regEofA = ++pParse->nMem;

   regAddrB = ++pParse->nMem;

   regEofB = ++pParse->nMem;

   regOutA = ++pParse->nMem;

   regOutB = ++pParse->nMem;

   sqlite3SelectDestInit(&destA, SRT_Coroutine, regAddrA);

   sqlite3SelectDestInit(&destB, SRT_Coroutine, regAddrB);

   /* Jump past the various subroutines and coroutines to the main

   ** merge loop

   */

   j1 = sqlite3VdbeAddOp0(v, OP_Goto);

   addrSelectA = sqlite3VdbeCurrentAddr(v);

   /* Generate a coroutine to evaluate the SELECT statement to the

   ** left of the compound operator - the "A" select.

   */

   VdbeNoopComment((v, "Begin coroutine for left SELECT"));

   pPrior->iLimit = regLimitA;

   sqlite3Select(pParse, pPrior, &destA);

   sqlite3VdbeAddOp2(v, OP_Integer, 1, regEofA);

   sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);

   VdbeNoopComment((v, "End coroutine for left SELECT"));

   /* Generate a coroutine to evaluate the SELECT statement on 

   ** the right - the "B" select

   */

   addrSelectB = sqlite3VdbeCurrentAddr(v);

   VdbeNoopComment((v, "Begin coroutine for right SELECT"));

   savedLimit = p->iLimit;

   savedOffset = p->iOffset;

   p->iLimit = regLimitB;

   p->iOffset = 0;  

   sqlite3Select(pParse, p, &destB);

   p->iLimit = savedLimit;

   p->iOffset = savedOffset;

   sqlite3VdbeAddOp2(v, OP_Integer, 1, regEofB);

   sqlite3VdbeAddOp1(v, OP_Yield, regAddrB);

   VdbeNoopComment((v, "End coroutine for right SELECT"));

   /* Generate a subroutine that outputs the current row of the A

   ** select as the next output row of the compound select.

   */

   VdbeNoopComment((v, "Output routine for A"));

   addrOutA = generateOutputSubroutine(pParse,

                  p, &destA, pDest, regOutA,

                  regPrev, pKeyDup, P4_KEYINFO_HANDOFF, labelEnd);

   /* Generate a subroutine that outputs the current row of the B

   ** select as the next output row of the compound select.

   */

   if( op==TK_ALL || op==TK_UNION ){

     VdbeNoopComment((v, "Output routine for B"));

     addrOutB = generateOutputSubroutine(pParse,

                  p, &destB, pDest, regOutB,

                  regPrev, pKeyDup, P4_KEYINFO_STATIC, labelEnd);

   }

   /* Generate a subroutine to run when the results from select A

   ** are exhausted and only data in select B remains.

   */

   VdbeNoopComment((v, "eof-A subroutine"));

   if( op==TK_EXCEPT || op==TK_INTERSECT ){

     addrEofA = sqlite3VdbeAddOp2(v, OP_Goto, 0, labelEnd);

   }else{  

     addrEofA = sqlite3VdbeAddOp2(v, OP_If, regEofB, labelEnd);

     sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);

     sqlite3VdbeAddOp1(v, OP_Yield, regAddrB);

     sqlite3VdbeAddOp2(v, OP_Goto, 0, addrEofA);

   }

   /* Generate a subroutine to run when the results from select B

   ** are exhausted and only data in select A remains.

   */

   if( op==TK_INTERSECT ){

     addrEofB = addrEofA;

   }else{  

     VdbeNoopComment((v, "eof-B subroutine"));

     addrEofB = sqlite3VdbeAddOp2(v, OP_If, regEofA, labelEnd);

     sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);

     sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);

     sqlite3VdbeAddOp2(v, OP_Goto, 0, addrEofB);

   }

   /* Generate code to handle the case of A<B

   */

   VdbeNoopComment((v, "A-lt-B subroutine"));

   addrAltB = sqlite3VdbeAddOp2(v, OP_Gosub, regOutA, addrOutA);

   sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);

   sqlite3VdbeAddOp2(v, OP_If, regEofA, addrEofA);

   sqlite3VdbeAddOp2(v, OP_Goto, 0, labelCmpr);

   /* Generate code to handle the case of A==B

   */

   if( op==TK_ALL ){

     addrAeqB = addrAltB;

   }else if( op==TK_INTERSECT ){

     addrAeqB = addrAltB;

     addrAltB++;

   }else{

     VdbeNoopComment((v, "A-eq-B subroutine"));

     addrAeqB =

     sqlite3VdbeAddOp1(v, OP_Yield, regAddrA);

     sqlite3VdbeAddOp2(v, OP_If, regEofA, addrEofA);

     sqlite3VdbeAddOp2(v, OP_Goto, 0, labelCmpr);

   }

   /* Generate code to handle the case of A>B

   */

   VdbeNoopComment((v, "A-gt-B subroutine"));

   addrAgtB = sqlite3VdbeCurrentAddr(v);

   if( op==TK_ALL || op==TK_UNION ){

     sqlite3VdbeAddOp2(v, OP_Gosub, regOutB, addrOutB);

   }

   sqlite3VdbeAddOp1(v, OP_Yield, regAddrB);

   sqlite3VdbeAddOp2(v, OP_If, regEofB, addrEofB);

   sqlite3VdbeAddOp2(v, OP_Goto, 0, labelCmpr);

   /* This code runs once to initialize everything.

   */

   sqlite3VdbeJumpHere(v, j1);

   sqlite3VdbeAddOp2(v, OP_Integer, 0, regEofA);

   sqlite3VdbeAddOp2(v, OP_Integer, 0, regEofB);

   sqlite3VdbeAddOp2(v, OP_Gosub, regAddrA, addrSelectA);

   sqlite3VdbeAddOp2(v, OP_Gosub, regAddrB, addrSelectB);

   sqlite3VdbeAddOp2(v, OP_If, regEofA, addrEofA);

   sqlite3VdbeAddOp2(v, OP_If, regEofB, addrEofB);

   /* Implement the main merge loop

   */

   sqlite3VdbeResolveLabel(v, labelCmpr);

   sqlite3VdbeAddOp4(v, OP_Permutation, 0, 0, 0, (char*)aPermute, P4_INTARRAY);

   sqlite3VdbeAddOp4(v, OP_Compare, destA.iMem, destB.iMem, nOrderBy,

                          (char*)pKeyMerge, P4_KEYINFO_HANDOFF);

   sqlite3VdbeAddOp3(v, OP_Jump, addrAltB, addrAeqB, addrAgtB);

   /* Release temporary registers

   */

   if( regPrev ){

     sqlite3ReleaseTempRange(pParse, regPrev, nOrderBy+1);

   }

   /* Jump to the this point in order to terminate the query.

   */

   sqlite3VdbeResolveLabel(v, labelEnd);

   /* Set the number of output columns

   */

   if( pDest->eDest==SRT_Output ){

     Select *pFirst = pPrior;

     while( pFirst->pPrior ) pFirst = pFirst->pPrior;

     generateColumnNames(pParse, 0, pFirst->pEList);

   }

   /* Reassembly the compound query so that it will be freed correctly

   ** by the calling function */

   if( p->pPrior ){

     sqlite3SelectDelete(db, p->pPrior);

   }

   p->pPrior = pPrior;

   /*** TBD:  Insert subroutine calls to close cursors on incomplete

   **** subqueries ****/

   return SQLITE_OK;

 }

 #endif

 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)

 /* Forward Declarations */

 static void substExprList(sqlite3*, ExprList*, int, ExprList*);

 static void substSelect(sqlite3*, Select *, int, ExprList *);

 /*

 ** Scan through the expression pExpr.  Replace every reference to

 ** a column in table number iTable with a copy of the iColumn-th

 ** entry in pEList.  (But leave references to the ROWID column 

 ** unchanged.)

 **

 ** This routine is part of the flattening procedure.  A subquery

 ** whose result set is defined by pEList appears as entry in the

 ** FROM clause of a SELECT such that the VDBE cursor assigned to that

 ** FORM clause entry is iTable.  This routine make the necessary 

 ** changes to pExpr so that it refers directly to the source table

 ** of the subquery rather the result set of the subquery.

 */

 static void substExpr(

   sqlite3 *db,        /* Report malloc errors to this connection */

   Expr *pExpr,        /* Expr in which substitution occurs */

   int iTable,         /* Table to be substituted */

   ExprList *pEList    /* Substitute expressions */

 ){

   if( pExpr==0 ) return;

   if( pExpr->op==TK_COLUMN && pExpr->iTable==iTable ){

     if( pExpr->iColumn<0 ){

       pExpr->op = TK_NULL;

     }else{

       Expr *pNew;

       assert( pEList!=0 && pExpr->iColumn<pEList->nExpr );

       assert( pExpr->pLeft==0 && pExpr->pRight==0 && pExpr->pList==0 );

       pNew = pEList->a[pExpr->iColumn].pExpr;

       assert( pNew!=0 );

       pExpr->op = pNew->op;

       assert( pExpr->pLeft==0 );

       pExpr->pLeft = sqlite3ExprDup(db, pNew->pLeft);

       assert( pExpr->pRight==0 );

       pExpr->pRight = sqlite3ExprDup(db, pNew->pRight);

       assert( pExpr->pList==0 );

       pExpr->pList = sqlite3ExprListDup(db, pNew->pList);

       pExpr->iTable = pNew->iTable;

       pExpr->pTab = pNew->pTab;

       pExpr->iColumn = pNew->iColumn;

       pExpr->iAgg = pNew->iAgg;

       sqlite3TokenCopy(db, &pExpr->token, &pNew->token);

       sqlite3TokenCopy(db, &pExpr->span, &pNew->span);

       pExpr->pSelect = sqlite3SelectDup(db, pNew->pSelect);

       pExpr->flags = pNew->flags;

     }

   }else{

     substExpr(db, pExpr->pLeft, iTable, pEList);

     substExpr(db, pExpr->pRight, iTable, pEList);

     substSelect(db, pExpr->pSelect, iTable, pEList);

     substExprList(db, pExpr->pList, iTable, pEList);

   }

 }

 static void substExprList(

   sqlite3 *db,         /* Report malloc errors here */

   ExprList *pList,     /* List to scan and in which to make substitutes */

   int iTable,          /* Table to be substituted */

   ExprList *pEList     /* Substitute values */

 ){

   int i;

   if( pList==0 ) return;

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

     substExpr(db, pList->a[i].pExpr, iTable, pEList);

   }

 }

 static void substSelect(

   sqlite3 *db,         /* Report malloc errors here */

   Select *p,           /* SELECT statement in which to make substitutions */

   int iTable,          /* Table to be replaced */

   ExprList *pEList     /* Substitute values */

 ){

   SrcList *pSrc;

   struct SrcList_item *pItem;

   int i;

   if( !p ) return;

   substExprList(db, p->pEList, iTable, pEList);

   substExprList(db, p->pGroupBy, iTable, pEList);

   substExprList(db, p->pOrderBy, iTable, pEList);

   substExpr(db, p->pHaving, iTable, pEList);

   substExpr(db, p->pWhere, iTable, pEList);

   substSelect(db, p->pPrior, iTable, pEList);

   pSrc = p->pSrc;

   if( pSrc ){

     for(i=pSrc->nSrc, pItem=pSrc->a; i>0; i--, pItem++){

       substSelect(db, pItem->pSelect, iTable, pEList);

     }

   }

 }

 #endif /* !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW) */

 #if !defined(SQLITE_OMIT_SUBQUERY) || !defined(SQLITE_OMIT_VIEW)

 /*

 ** This routine attempts to flatten subqueries in order to speed

 ** execution.  It returns 1 if it makes changes and 0 if no flattening

 ** occurs.

 **

 ** To understand the concept of flattening, consider the following

 ** query:

 **

 **     SELECT a FROM (SELECT x+y AS a FROM t1 WHERE z<100) WHERE a>5

 **

 ** The default way of implementing this query is to execute the

 ** subquery first and store the results in a temporary table, then

 ** run the outer query on that temporary table.  This requires two

 ** passes over the data.  Furthermore, because the temporary table

 ** has no indices, the WHERE clause on the outer query cannot be

 ** optimized.

 **

 ** This routine attempts to rewrite queries such as the above into

 ** a single flat select, like this:

 **

 **     SELECT x+y AS a FROM t1 WHERE z<100 AND a>5

 **

 ** The code generated for this simpification gives the same result

 ** but only has to scan the data once.  And because indices might 

 ** exist on the table t1, a complete scan of the data might be

 ** avoided.

 **

 ** Flattening is only attempted if all of the following are true:

 **

 **   (1)  The subquery and the outer query do not both use aggregates.

 **

 **   (2)  The subquery is not an aggregate or the outer query is not a join.

 **

 **   (3)  The subquery is not the right operand of a left outer join

 **        (Originally ticket #306.  Strenghtened by ticket #3300)

 **

 **   (4)  The subquery is not DISTINCT or the outer query is not a join.

 **

 **   (5)  The subquery is not DISTINCT or the outer query does not use

 **        aggregates.

 **

 **   (6)  The subquery does not use aggregates or the outer query is not

 **        DISTINCT.

 **

 **   (7)  The subquery has a FROM clause.

 **

 **   (8)  The subquery does not use LIMIT or the outer query is not a join.

 **

 **   (9)  The subquery does not use LIMIT or the outer query does not use

 **        aggregates.

 **

 **  (10)  The subquery does not use aggregates or the outer query does not

 **        use LIMIT.

 **

 **  (11)  The subquery and the outer query do not both have ORDER BY clauses.

 **

 **  (12)  Not implemented.  Subsumed into restriction (3).  Was previously

 **        a separate restriction deriving from ticket #350.

 **

 **  (13)  The subquery and outer query do not both use LIMIT

 **

 **  (14)  The subquery does not use OFFSET

 **

 **  (15)  The outer query is not part of a compound select or the

 **        subquery does not have both an ORDER BY and a LIMIT clause.

 **        (See ticket #2339)

 **

 **  (16)  The outer query is not an aggregate or the subquery does

 **        not contain ORDER BY.  (Ticket #2942)  This used to not matter

 **        until we introduced the group_concat() function.  

 **

 **  (17)  The sub-query is not a compound select, or it is a UNION ALL 

 **        compound clause made up entirely of non-aggregate queries, and 

 **        the parent query:

 **

 **          * is not itself part of a compound select,

 **          * is not an aggregate or DISTINCT query, and

 **          * has no other tables or sub-selects in the FROM clause.

 **

 **        The parent and sub-query may contain WHERE clauses. Subject to

 **        rules (11), (13) and (14), they may also contain ORDER BY,

 **        LIMIT and OFFSET clauses.

 **

 **  (18)  If the sub-query is a compound select, then all terms of the

 **        ORDER by clause of the parent must be simple references to 

 **        columns of the sub-query.

 **

 **  (19)  The subquery does not use LIMIT or the outer query does not

 **        have a WHERE clause.

 **

 ** In this routine, the "p" parameter is a pointer to the outer query.

 ** The subquery is p->pSrc->a[iFrom].  isAgg is true if the outer query

 ** uses aggregates and subqueryIsAgg is true if the subquery uses aggregates.

 **

 ** If flattening is not attempted, this routine is a no-op and returns 0.

 ** If flattening is attempted this routine returns 1.

 **

 ** All of the expression analysis must occur on both the outer query and

 ** the subquery before this routine runs.

 */

 static int flattenSubquery(

   Parse *pParse,       /* Parsing context */

   Select *p,           /* The parent or outer SELECT statement */

   int iFrom,           /* Index in p->pSrc->a[] of the inner subquery */

   int isAgg,           /* True if outer SELECT uses aggregate functions */

   int subqueryIsAgg    /* True if the subquery uses aggregate functions */

 ){

   const char *zSavedAuthContext = pParse->zAuthContext;

   Select *pParent;

   Select *pSub;       /* The inner query or "subquery" */

   Select *pSub1;      /* Pointer to the rightmost select in sub-query */

   SrcList *pSrc;      /* The FROM clause of the outer query */

   SrcList *pSubSrc;   /* The FROM clause of the subquery */

   ExprList *pList;    /* The result set of the outer query */

   int iParent;        /* VDBE cursor number of the pSub result set temp table */

   int i;              /* Loop counter */

   Expr *pWhere;                    /* The WHERE clause */

   struct SrcList_item *pSubitem;   /* The subquery */

   sqlite3 *db = pParse->db;

   /* Check to see if flattening is permitted.  Return 0 if not.

   */

   if( p==0 ) return 0;

   pSrc = p->pSrc;

   assert( pSrc && iFrom>=0 && iFrom<pSrc->nSrc );

   pSubitem = &pSrc->a[iFrom];

   iParent = pSubitem->iCursor;

   pSub = pSubitem->pSelect;

   assert( pSub!=0 );

   if( isAgg && subqueryIsAgg ) return 0;                 /* Restriction (1)  */

   if( subqueryIsAgg && pSrc->nSrc>1 ) return 0;          /* Restriction (2)  */

   pSubSrc = pSub->pSrc;

   assert( pSubSrc );

   /* Prior to version 3.1.2, when LIMIT and OFFSET had to be simple constants,

   ** not arbitrary expresssions, we allowed some combining of LIMIT and OFFSET

   ** because they could be computed at compile-time.  But when LIMIT and OFFSET

   ** became arbitrary expressions, we were forced to add restrictions (13)

   ** and (14). */

   if( pSub->pLimit && p->pLimit ) return 0;              /* Restriction (13) */

   if( pSub->pOffset ) return 0;                          /* Restriction (14) */

   if( p->pRightmost && pSub->pLimit && pSub->pOrderBy ){

     return 0;                                            /* Restriction (15) */

   }

   if( pSubSrc->nSrc==0 ) return 0;                       /* Restriction (7)  */

   if( ((pSub->selFlags & SF_Distinct)!=0 || pSub->pLimit) 

          && (pSrc->nSrc>1 || isAgg) ){          /* Restrictions (4)(5)(8)(9) */

      return 0;       

   }

   if( (p->selFlags & SF_Distinct)!=0 && subqueryIsAgg ){

      return 0;         /* Restriction (6)  */

   }

   if( p->pOrderBy && pSub->pOrderBy ){

      return 0;                                           /* Restriction (11) */

   }

   if( isAgg && pSub->pOrderBy ) return 0;                /* Restriction (16) */

   if( pSub->pLimit && p->pWhere ) return 0;              /* Restriction (19) */

   /* OBSOLETE COMMENT 1:

   ** Restriction 3:  If the subquery is a join, make sure the subquery is 

   ** not used as the right operand of an outer join.  Examples of why this

   ** is not allowed:

   **

   **         t1 LEFT OUTER JOIN (t2 JOIN t3)

   **

   ** If we flatten the above, we would get

   **

   **         (t1 LEFT OUTER JOIN t2) JOIN t3

   **

   ** which is not at all the same thing.

   **

   ** OBSOLETE COMMENT 2:

   ** Restriction 12:  If the subquery is the right operand of a left outer

   ** join, make sure the subquery has no WHERE clause.

   ** An examples of why this is not allowed:

   **

   **         t1 LEFT OUTER JOIN (SELECT * FROM t2 WHERE t2.x>0)

   **

   ** If we flatten the above, we would get

   **

   **         (t1 LEFT OUTER JOIN t2) WHERE t2.x>0

   **

   ** But the t2.x>0 test will always fail on a NULL row of t2, which

   ** effectively converts the OUTER JOIN into an INNER JOIN.

   **

   ** THIS OVERRIDES OBSOLETE COMMENTS 1 AND 2 ABOVE:

   ** Ticket #3300 shows that flattening the right term of a LEFT JOIN

   ** is fraught with danger.  Best to avoid the whole thing.  If the

   ** subquery is the right term of a LEFT JOIN, then do not flatten.

   */

   if( (pSubitem->jointype & JT_OUTER)!=0 ){

     return 0;

   }

   /* Restriction 17: If the sub-query is a compound SELECT, then it must

   ** use only the UNION ALL operator. And none of the simple select queries

   ** that make up the compound SELECT are allowed to be aggregate or distinct

   ** queries.

   */

   if( pSub->pPrior ){

     if( p->pPrior || isAgg || (p->selFlags & SF_Distinct)!=0 || pSrc->nSrc!=1 ){

       return 0;