src/select.c

/*
** 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 1.85 2002/05/25 00:18:21 drh Exp $
*/
#include "sqliteInt.h"

/*
** Allocate a new Select structure and return a pointer to that
** structure.
*/
Select *sqliteSelectNew(
  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 */
  int nLimit,           /* LIMIT value.  -1 means not used */
  int nOffset           /* OFFSET value.  -1 means not used */
){
  Select *pNew;
  pNew = sqliteMalloc( sizeof(*pNew) );
  if( pNew==0 ){
    sqliteExprListDelete(pEList);
    sqliteSrcListDelete(pSrc);
    sqliteExprDelete(pWhere);
    sqliteExprListDelete(pGroupBy);
    sqliteExprDelete(pHaving);
    sqliteExprListDelete(pOrderBy);
  }else{
    pNew->pEList = pEList;
    pNew->pSrc = pSrc;
    pNew->pWhere = pWhere;
    pNew->pGroupBy = pGroupBy;
    pNew->pHaving = pHaving;
    pNew->pOrderBy = pOrderBy;
    pNew->isDistinct = isDistinct;
    pNew->op = TK_SELECT;
    pNew->nLimit = nLimit;
    pNew->nOffset = nOffset;
  }
  return pNew;
}

/*
** 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_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 sqliteJoinType(Parse *pParse, Token *pA, Token *pB, Token *pC){
  int jointype = 0;
  Token *apAll[3];
  Token *p;
  static struct {
    const char *zKeyword;
    int nChar;
    int 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 },
  };
  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 
          && sqliteStrNICmp(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
  ){
    static Token dummy = { 0, 0 };
    char *zSp1 = " ", *zSp2 = " ";
    if( pB==0 ){ pB = &dummy; zSp1 = 0; }
    if( pC==0 ){ pC = &dummy; zSp2 = 0; }
    sqliteSetNString(&pParse->zErrMsg, "unknown or unsupported join type: ", 0,
       pA->z, pA->n, zSp1, 1, pB->z, pB->n, zSp2, 1, pC->z, pC->n, 0);
    pParse->nErr++;
    jointype = JT_INNER;
  }else if( jointype & JT_RIGHT ){
    sqliteSetString(&pParse->zErrMsg, 
      "RIGHT and FULL OUTER JOINs are not currently supported", 0);
    pParse->nErr++;
    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( sqliteStrICmp(pTab->aCol[i].zName, zCol)==0 ) return i;
  }
  return -1;
}

/*
** 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(
  const char *zCol,        /* Name of the column */
  const Table *pTab1,      /* First table */
  const Table *pTab2,      /* Second table */
  Expr **ppExpr            /* Add the equality term to this expression */
){
  Token dummy;
  Expr *pE1a, *pE1b, *pE1c;
  Expr *pE2a, *pE2b, *pE2c;
  Expr *pE;

  dummy.z = zCol;
  dummy.n = strlen(zCol);
  pE1a = sqliteExpr(TK_ID, 0, 0, &dummy);
  pE2a = sqliteExpr(TK_ID, 0, 0, &dummy);
  dummy.z = pTab1->zName;
  dummy.n = strlen(dummy.z);
  pE1b = sqliteExpr(TK_ID, 0, 0, &dummy);
  dummy.z = pTab2->zName;
  dummy.n = strlen(dummy.z);
  pE2b = sqliteExpr(TK_ID, 0, 0, &dummy);
  pE1c = sqliteExpr(TK_DOT, pE1b, pE1a, 0);
  pE2c = sqliteExpr(TK_DOT, pE2b, pE2a, 0);
  pE = sqliteExpr(TK_EQ, pE1c, pE2c, 0);
  if( *ppExpr ){
    *ppExpr = sqliteExpr(TK_AND, *ppExpr, pE, 0);
  }else{
    *ppExpr = pE;
  }
}

/*
** 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.
**
** This routine returns the number of errors encountered.
*/
static int sqliteProcessJoin(Parse *pParse, Select *p){
  SrcList *pSrc;
  int i, j;
  pSrc = p->pSrc;
  for(i=0; i<pSrc->nSrc-1; i++){
    struct SrcList_item *pTerm = &pSrc->a[i];
    struct SrcList_item *pOther = &pSrc->a[i+1];

    if( pTerm->pTab==0 || pOther->pTab==0 ) continue;

    /* When the NATURAL keyword is present, add WHERE clause terms for
    ** every column that the two tables have in common.
    */
    if( pTerm->jointype & JT_NATURAL ){
      Table *pTab;
      if( pTerm->pOn || pTerm->pUsing ){
        sqliteSetString(&pParse->zErrMsg, "a NATURAL join may not have "
           "an ON or USING clause", 0);
        pParse->nErr++;
        return 1;
      }
      pTab = pTerm->pTab;
      for(j=0; j<pTab->nCol; j++){
        if( columnIndex(pOther->pTab, pTab->aCol[j].zName)>=0 ){
          addWhereTerm(pTab->aCol[j].zName, pTab, pOther->pTab, &p->pWhere);
        }
      }
    }

    /* Disallow both ON and USING clauses in the same join
    */
    if( pTerm->pOn && pTerm->pUsing ){
      sqliteSetString(&pParse->zErrMsg, "cannot have both ON and USING "
        "clauses in the same join", 0);
      pParse->nErr++;
      return 1;
    }

    /* Add the ON clause to the end of the WHERE clause, connected by
    ** and AND operator.
    */
    if( pTerm->pOn ){
      if( p->pWhere==0 ){
        p->pWhere = pTerm->pOn;
      }else{
        p->pWhere = sqliteExpr(TK_AND, p->pWhere, pTerm->pOn, 0);
      }
      pTerm->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( pTerm->pUsing ){
      IdList *pList;
      int j;
      assert( i<pSrc->nSrc-1 );
      pList = pTerm->pUsing;
      for(j=0; j<pList->nId; j++){
        if( columnIndex(pTerm->pTab, pList->a[i].zName)<0 ||
            columnIndex(pOther->pTab, pList->a[i].zName)<0 ){
          sqliteSetString(&pParse->zErrMsg, "cannot join using column ",
            pList->a[i].zName, " - column not present in both tables", 0);
          pParse->nErr++;
          return 1;
        }
        addWhereTerm(pList->a[i].zName, pTerm->pTab, pOther->pTab, &p->pWhere);
      }
    }
  }
  return 0;
}

/*
** Delete the given Select structure and all of its substructures.
*/
void sqliteSelectDelete(Select *p){
  if( p==0 ) return;
  sqliteExprListDelete(p->pEList);
  sqliteSrcListDelete(p->pSrc);
  sqliteExprDelete(p->pWhere);
  sqliteExprListDelete(p->pGroupBy);
  sqliteExprDelete(p->pHaving);
  sqliteExprListDelete(p->pOrderBy);
  sqliteSelectDelete(p->pPrior);
  sqliteFree(p->zSelect);
  sqliteFree(p);
}

/*
** Delete the aggregate information from the parse structure.
*/
static void sqliteAggregateInfoReset(Parse *pParse){
  sqliteFree(pParse->aAgg);
  pParse->aAgg = 0;
  pParse->nAgg = 0;
  pParse->useAgg = 0;
}

/*
** This routine generates the code for the inside of the inner loop
** of a SELECT.
**
** The pEList is used to determine the values for each column in the
** result row.  Except  if pEList==NULL, then we just read nColumn
** elements from the srcTab table.
*/
static int selectInnerLoop(
  Parse *pParse,          /* The parser context */
  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 */
  int eDest,              /* How to dispose of the results */
  int iParm,              /* An argument to the disposal method */
  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;
  if( v==0 ) return 0;

  /* Pull the requested columns.
  */
  if( pEList ){
    for(i=0; i<pEList->nExpr; i++){
      sqliteExprCode(pParse, pEList->a[i].pExpr);
    }
    nColumn = pEList->nExpr;
  }else{
    for(i=0; i<nColumn; i++){
      sqliteVdbeAddOp(v, OP_Column, srcTab, i);
    }
  }

  /* 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( distinct>=0 ){
    int lbl = sqliteVdbeMakeLabel(v);
    sqliteVdbeAddOp(v, OP_MakeKey, pEList->nExpr, 1);
    sqliteVdbeAddOp(v, OP_Distinct, distinct, lbl);
    sqliteVdbeAddOp(v, OP_Pop, pEList->nExpr+1, 0);
    sqliteVdbeAddOp(v, OP_Goto, 0, iContinue);
    sqliteVdbeResolveLabel(v, lbl);
    sqliteVdbeAddOp(v, OP_String, 0, 0);
    sqliteVdbeAddOp(v, OP_PutStrKey, distinct, 0);
  }

  /* If there is an ORDER BY clause, then store the results
  ** in a sorter.
  */
  if( pOrderBy ){
    char *zSortOrder;
    sqliteVdbeAddOp(v, OP_SortMakeRec, nColumn, 0);
    zSortOrder = sqliteMalloc( pOrderBy->nExpr + 1 );
    if( zSortOrder==0 ) return 1;
    for(i=0; i<pOrderBy->nExpr; i++){
      zSortOrder[i] = pOrderBy->a[i].sortOrder ? '-' : '+';
      sqliteExprCode(pParse, pOrderBy->a[i].pExpr);
    }
    zSortOrder[pOrderBy->nExpr] = 0;
    sqliteVdbeAddOp(v, OP_SortMakeKey, pOrderBy->nExpr, 0);
    sqliteVdbeChangeP3(v, -1, zSortOrder, strlen(zSortOrder));
    sqliteFree(zSortOrder);
    sqliteVdbeAddOp(v, OP_SortPut, 0, 0);
  }else 

  /* In this mode, write each query result to the key of the temporary
  ** table iParm.
  */
  if( eDest==SRT_Union ){
    sqliteVdbeAddOp(v, OP_MakeRecord, nColumn, 0);
    sqliteVdbeAddOp(v, OP_String, iParm, 0);
    sqliteVdbeAddOp(v, OP_PutStrKey, iParm, 0);
  }else 

  /* Store the result as data using a unique key.
  */
  if( eDest==SRT_Table || eDest==SRT_TempTable ){
    sqliteVdbeAddOp(v, OP_MakeRecord, nColumn, 0);
    sqliteVdbeAddOp(v, OP_NewRecno, iParm, 0);
    sqliteVdbeAddOp(v, OP_Pull, 1, 0);
    sqliteVdbeAddOp(v, OP_PutIntKey, iParm, 0);
  }else 

  /* 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.
  */
  if( eDest==SRT_Except ){
    int addr = sqliteVdbeAddOp(v, OP_MakeRecord, nColumn, 0);
    sqliteVdbeAddOp(v, OP_NotFound, iParm, addr+3);
    sqliteVdbeAddOp(v, OP_Delete, iParm, 0);
  }else 

  /* 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.
  */
  if( eDest==SRT_Set ){
    assert( nColumn==1 );
    sqliteVdbeAddOp(v, OP_String, 0, 0);
    sqliteVdbeAddOp(v, OP_PutStrKey, iParm, 0);
  }else 


  /* 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.
  */
  if( eDest==SRT_Mem ){
    assert( nColumn==1 );
    sqliteVdbeAddOp(v, OP_MemStore, iParm, 1);
    sqliteVdbeAddOp(v, OP_Goto, 0, iBreak);
  }else

  /* If none of the above, send the data to the callback function.
  */
  {
    sqliteVdbeAddOp(v, OP_Callback, nColumn, iBreak);
  }
  return 0;
}

/*
** 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(Vdbe *v, int nColumn){
  int end = sqliteVdbeMakeLabel(v);
  int addr;
  sqliteVdbeAddOp(v, OP_Sort, 0, 0);
  addr = sqliteVdbeAddOp(v, OP_SortNext, 0, end);
  sqliteVdbeAddOp(v, OP_SortCallback, nColumn, end);
  sqliteVdbeAddOp(v, OP_Goto, 0, addr);
  sqliteVdbeResolveLabel(v, end);
  sqliteVdbeAddOp(v, OP_SortReset, 0, 0);
}

/*
** Generate code that will tell the VDBE how many columns there
** are in the result and the name for each column.  This information
** is used to provide "argc" and "azCol[]" values in the callback.
*/
static void generateColumnNames(
  Parse *pParse,      /* Parser context */
  int base,           /* VDBE cursor corresponding to first entry in pTabList */
  SrcList *pTabList,  /* List of tables */
  ExprList *pEList    /* Expressions defining the result set */
){
  Vdbe *v = pParse->pVdbe;
  int i;
  if( pParse->colNamesSet || v==0 || sqlite_malloc_failed ) return;
  pParse->colNamesSet = 1;
  sqliteVdbeAddOp(v, OP_ColumnCount, pEList->nExpr, 0);
  for(i=0; i<pEList->nExpr; i++){
    Expr *p;
    int showFullNames;
    if( pEList->a[i].zName ){
      char *zName = pEList->a[i].zName;
      sqliteVdbeAddOp(v, OP_ColumnName, i, 0);
      sqliteVdbeChangeP3(v, -1, zName, strlen(zName));
      continue;
    }
    p = pEList->a[i].pExpr;
    if( p==0 ) continue;
    showFullNames = (pParse->db->flags & SQLITE_FullColNames)!=0;
    if( p->span.z && p->span.z[0] && !showFullNames ){
      int addr = sqliteVdbeAddOp(v,OP_ColumnName, i, 0);
      sqliteVdbeChangeP3(v, -1, p->span.z, p->span.n);
      sqliteVdbeCompressSpace(v, addr);
    }else if( p->op==TK_COLUMN && pTabList ){
      Table *pTab = pTabList->a[p->iTable - base].pTab;
      char *zCol;
      int iCol = p->iColumn;
      if( iCol<0 ) iCol = pTab->iPKey;
      assert( iCol==-1 || (iCol>=0 && iCol<pTab->nCol) );
      zCol = iCol<0 ? "_ROWID_" : pTab->aCol[iCol].zName;
      if( pTabList->nSrc>1 || showFullNames ){
        char *zName = 0;
        char *zTab;
 
        zTab = pTabList->a[p->iTable - base].zAlias;
        if( showFullNames || zTab==0 ) zTab = pTab->zName;
        sqliteSetString(&zName, zTab, ".", zCol, 0);
        sqliteVdbeAddOp(v, OP_ColumnName, i, 0);
        sqliteVdbeChangeP3(v, -1, zName, strlen(zName));
        sqliteFree(zName);
      }else{
        sqliteVdbeAddOp(v, OP_ColumnName, i, 0);
        sqliteVdbeChangeP3(v, -1, zCol, 0);
      }
    }else if( p->span.z && p->span.z[0] ){
      int addr = sqliteVdbeAddOp(v,OP_ColumnName, i, 0);
      sqliteVdbeChangeP3(v, -1, p->span.z, p->span.n);
      sqliteVdbeCompressSpace(v, addr);
    }else{
      char zName[30];
      assert( p->op!=TK_COLUMN || pTabList==0 );
      sprintf(zName, "column%d", i+1);
      sqliteVdbeAddOp(v, OP_ColumnName, i, 0);
      sqliteVdbeChangeP3(v, -1, zName, strlen(zName));
    }
  }
}

/*
** 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;
}

/*
** Given a SELECT statement, generate a Table structure that describes
** the result set of that SELECT.
*/
Table *sqliteResultSetOfSelect(Parse *pParse, char *zTabName, Select *pSelect){
  Table *pTab;
  int i;
  ExprList *pEList;
  static int fillInColumnList(Parse*, Select*);

  if( fillInColumnList(pParse, pSelect) ){
    return 0;
  }
  pTab = sqliteMalloc( sizeof(Table) );
  if( pTab==0 ){
    return 0;
  }
  pTab->zName = zTabName ? sqliteStrDup(zTabName) : 0;
  pEList = pSelect->pEList;
  pTab->nCol = pEList->nExpr;
  assert( pTab->nCol>0 );
  pTab->aCol = sqliteMalloc( sizeof(pTab->aCol[0])*pTab->nCol );
  for(i=0; i<pTab->nCol; i++){
    Expr *p;
    if( pEList->a[i].zName ){
      pTab->aCol[i].zName = sqliteStrDup(pEList->a[i].zName);
    }else if( (p=pEList->a[i].pExpr)->span.z && p->span.z[0] ){
      sqliteSetNString(&pTab->aCol[i].zName, p->span.z, p->span.n, 0);
    }else if( p->op==TK_DOT && p->pRight && p->pRight->token.z &&
           p->pRight->token.z[0] ){
      sqliteSetNString(&pTab->aCol[i].zName, 
           p->pRight->token.z, p->pRight->token.n, 0);
    }else{
      char zBuf[30];
      sprintf(zBuf, "column%d", i+1);
      pTab->aCol[i].zName = sqliteStrDup(zBuf);
    }
  }
  pTab->iPKey = -1;
  return pTab;
}

/*
** For the given SELECT statement, do three things.
**
**    (1)  Fill in the pTabList->a[].pTab fields in the SrcList that 
**         defines the set of tables that should be scanned. 
**
**    (2)  Add terms to the WHERE clause to accomodate the NATURAL keyword
**         on joins and the ON and USING clause of joins.
**
**    (3)  Scan the list of columns in the result set (pEList) looking
**         for instances of the "*" operator or the TABLE.* operator.
**         If found, expand each "*" to be every column in every table
**         and TABLE.* to be every column in TABLE.
**
** Return 0 on success.  If there are problems, leave an error message
** in pParse and return non-zero.
*/
static int fillInColumnList(Parse *pParse, Select *p){
  int i, j, k, rc;
  SrcList *pTabList;
  ExprList *pEList;
  Table *pTab;

  if( p==0 || p->pSrc==0 ) return 1;
  pTabList = p->pSrc;
  pEList = p->pEList;

  /* Look up every table in the table list.
  */
  for(i=0; i<pTabList->nSrc; i++){
    if( pTabList->a[i].pTab ){
      /* This routine has run before!  No need to continue */
      return 0;
    }
    if( pTabList->a[i].zName==0 ){
      /* A sub-query in the FROM clause of a SELECT */
      assert( pTabList->a[i].pSelect!=0 );
      if( pTabList->a[i].zAlias==0 ){
        char zFakeName[60];
        sprintf(zFakeName, "sqlite_subquery_%p_",
           (void*)pTabList->a[i].pSelect);
        sqliteSetString(&pTabList->a[i].zAlias, zFakeName, 0);
      }
      pTabList->a[i].pTab = pTab = 
        sqliteResultSetOfSelect(pParse, pTabList->a[i].zAlias,
                                        pTabList->a[i].pSelect);
      if( pTab==0 ){
        return 1;
      }
      pTab->isTransient = 1;
    }else{
      /* An ordinary table or view name in the FROM clause */
      pTabList->a[i].pTab = pTab = 
        sqliteFindTable(pParse->db, pTabList->a[i].zName);
      if( pTab==0 ){
        sqliteSetString(&pParse->zErrMsg, "no such table: ", 
           pTabList->a[i].zName, 0);
        pParse->nErr++;
        return 1;
      }
      if( pTab->pSelect ){
        if( sqliteViewGetColumnNames(pParse, pTab) ){
          return 1;
        }
        pTabList->a[i].pSelect = sqliteSelectDup(pTab->pSelect);
      }
    }
  }

  /* Process NATURAL keywords, and ON and USING clauses of joins.
  */
  if( sqliteProcessJoin(pParse, p) ) return 1;

  /* For every "*" that occurs in the column list, insert the names of
  ** all columns in all tables.  And for every TABLE.* insert the names
  ** of all columns in TABLE.  The parser inserted a special expression
  ** with the TK_ALL operator for each "*" that it found in the column list.
  ** The following code just has to locate the TK_ALL expressions and expand
  ** each one to the list of all columns in all tables.
  **
  ** The first loop just checks to see if there are any "*" operators
  ** that need expanding.
  */
  for(k=0; k<pEList->nExpr; k++){
    Expr *pE = pEList->a[k].pExpr;
    if( pE->op==TK_ALL ) break;
    if( pE->op==TK_DOT && pE->pRight && pE->pRight->op==TK_ALL
         && pE->pLeft && pE->pLeft->op==TK_ID ) break;
  }
  rc = 0;
  if( k<pEList->nExpr ){
    /*
    ** If we get here it means the result set contains one or more "*"
    ** operators that need to be expanded.  Loop through each expression
    ** in the result set and expand them one by one.
    */
    struct ExprList_item *a = pEList->a;
    ExprList *pNew = 0;
    for(k=0; k<pEList->nExpr; k++){
      Expr *pE = a[k].pExpr;
      if( pE->op!=TK_ALL &&
           (pE->op!=TK_DOT || pE->pRight==0 || pE->pRight->op!=TK_ALL) ){
        /* This particular expression does not need to be expanded.
        */
        pNew = sqliteExprListAppend(pNew, a[k].pExpr, 0);
        pNew->a[pNew->nExpr-1].zName = a[k].zName;
        a[k].pExpr = 0;
        a[k].zName = 0;
      }else{
        /* This expression is a "*" or a "TABLE.*" and needs to be
        ** expanded. */
        int tableSeen = 0;      /* Set to 1 when TABLE matches */
        Token *pName;           /* text of name of TABLE */
        if( pE->op==TK_DOT && pE->pLeft ){
          pName = &pE->pLeft->token;
        }else{
          pName = 0;
        }
        for(i=0; i<pTabList->nSrc; i++){
          Table *pTab = pTabList->a[i].pTab;
          char *zTabName = pTabList->a[i].zAlias;
          if( zTabName==0 || zTabName[0]==0 ){ 
            zTabName = pTab->zName;
          }
          if( pName && (zTabName==0 || zTabName[0]==0 ||
                sqliteStrNICmp(pName->z, zTabName, pName->n)!=0) ){
            continue;
          }
          tableSeen = 1;
          for(j=0; j<pTab->nCol; j++){
            Expr *pExpr, *pLeft, *pRight;
            char *zName = pTab->aCol[j].zName;

            if( i>0 && (pTabList->a[i-1].jointype & JT_NATURAL)!=0 &&
                columnIndex(pTabList->a[i-1].pTab, zName)>=0 ){
              /* In a NATURAL join, omit the join columns from the 
              ** table on the right */
              continue;
            }
            if( i>0 && sqliteIdListIndex(pTabList->a[i-1].pUsing, zName)>=0 ){
              /* In a join with a USING clause, omit columns in the
              ** using clause from the table on the right. */
              continue;
            }
            pRight = sqliteExpr(TK_ID, 0, 0, 0);
            if( pRight==0 ) break;
            pRight->token.z = zName;
            pRight->token.n = strlen(zName);
            if( zTabName ){
              pLeft = sqliteExpr(TK_ID, 0, 0, 0);
              if( pLeft==0 ) break;
              pLeft->token.z = zTabName;
              pLeft->token.n = strlen(zTabName);
              pExpr = sqliteExpr(TK_DOT, pLeft, pRight, 0);
              if( pExpr==0 ) break;
            }else{
              pExpr = pRight;
              pExpr->span = pExpr->token;
            }
            pNew = sqliteExprListAppend(pNew, pExpr, 0);
          }
        }
        if( !tableSeen ){
          assert( pName!=0 );
          sqliteSetNString(&pParse->zErrMsg, "no such table: ", -1, 
            pName->z, pName->n, 0);
          rc = 1;
        }
      }
    }
    sqliteExprListDelete(pEList);
    p->pEList = pNew;
  }
  return rc;
}

/*
** This routine recursively unlinks the Select.pSrc.a[].pTab pointers
** in a select structure.  It just sets the pointers to NULL.  This
** routine is recursive in the sense that if the Select.pSrc.a[].pSelect
** pointer is not NULL, this routine is called recursively on that pointer.
**
** This routine is called on the Select structure that defines a
** VIEW in order to undo any bindings to tables.  This is necessary
** because those tables might be DROPed by a subsequent SQL command.
*/
void sqliteSelectUnbind(Select *p){
  int i;
  SrcList *pSrc = p->pSrc;
  Table *pTab;
  if( p==0 ) return;
  for(i=0; i<pSrc->nSrc; i++){
    if( (pTab = pSrc->a[i].pTab)!=0 ){
      if( pTab->isTransient ){
        sqliteDeleteTable(0, pTab);
        sqliteSelectDelete(pSrc->a[i].pSelect);
        pSrc->a[i].pSelect = 0;
      }
      pSrc->a[i].pTab = 0;
      if( pSrc->a[i].pSelect ){
        sqliteSelectUnbind(pSrc->a[i].pSelect);
      }
    }
  }
}

/*
** This routine associates entries in an ORDER BY expression list with
** columns in a result.  For each ORDER BY expression, the opcode of
** the top-level node is changed to TK_COLUMN and the iColumn value of
** the top-level node is filled in with column number and the iTable
** value of the top-level node is filled with iTable parameter.
**
** If there are prior SELECT clauses, they are processed first.  A match
** in an earlier SELECT takes precedence over a later SELECT.
**
** Any entry that does not match is flagged as an error.  The number
** of errors is returned.
*/
static int matchOrderbyToColumn(
  Parse *pParse,          /* A place to leave error messages */
  Select *pSelect,        /* Match to result columns of this SELECT */
  ExprList *pOrderBy,     /* The ORDER BY values to match against columns */
  int iTable,             /* Insert this this value in iTable */
  int mustComplete        /* If TRUE all ORDER BYs must match */
){
  int nErr = 0;
  int i, j;
  ExprList *pEList;

  if( pSelect==0 || pOrderBy==0 ) return 1;
  if( mustComplete ){
    for(i=0; i<pOrderBy->nExpr; i++){ pOrderBy->a[i].done = 0; }
  }
  if( fillInColumnList(pParse, pSelect) ){
    return 1;
  }
  if( pSelect->pPrior ){
    if( matchOrderbyToColumn(pParse, pSelect->pPrior, pOrderBy, iTable, 0) ){
      return 1;
    }
  }
  pEList = pSelect->pEList;
  for(i=0; i<pOrderBy->nExpr; i++){
    Expr *pE = pOrderBy->a[i].pExpr;
    int match = 0;
    if( pOrderBy->a[i].done ) continue;
    for(j=0; j<pEList->nExpr; j++){
      if( pEList->a[j].zName && (pE->op==TK_ID || pE->op==TK_STRING) ){
        char *zName, *zLabel;
        zName = pEList->a[j].zName;
        assert( pE->token.z );
        zLabel = sqliteStrNDup(pE->token.z, pE->token.n);
        sqliteDequote(zLabel);
        if( sqliteStrICmp(zName, zLabel)==0 ){ 
          match = 1; 
        }
        sqliteFree(zLabel);
      }
      if( match==0 && sqliteExprCompare(pE, pEList->a[j].pExpr) ){
        match = 1;
      }
      if( match ){
        pE->op = TK_COLUMN;
        pE->iColumn = j;
        pE->iTable = iTable;
        pOrderBy->a[i].done = 1;
        break;
      }
    }
    if( !match && mustComplete ){
      char zBuf[30];
      sprintf(zBuf,"%d",i+1);
      sqliteSetString(&pParse->zErrMsg, "ORDER BY term number ", zBuf, 
        " does not match any result column", 0);
      pParse->nErr++;
      nErr++;
      break;
    }
  }
  return nErr;  
}

/*
** 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 *sqliteGetVdbe(Parse *pParse){
  Vdbe *v = pParse->pVdbe;
  if( v==0 ){
    v = pParse->pVdbe = sqliteVdbeCreate(pParse->db);
  }
  return v;
}
    

/*
** This routine is called to process a query that is really the union
** or intersection of two or more separate queries.
*/
static int multiSelect(Parse *pParse, Select *p, int eDest, int iParm){
  int rc;             /* Success code from a subroutine */
  Select *pPrior;     /* Another SELECT immediately to our left */
  Vdbe *v;            /* Generate code to this VDBE */
  int base;           /* Baseline value for pParse->nTab */

  /* Make sure there is no ORDER BY clause on prior SELECTs.  Only the 
  ** last SELECT in the series may have an ORDER BY.
  */
  if( p==0 || p->pPrior==0 ) return 1;
  pPrior = p->pPrior;
  if( pPrior->pOrderBy ){
    sqliteSetString(&pParse->zErrMsg,"ORDER BY clause should come after ",
      selectOpName(p->op), " not before", 0);
    pParse->nErr++;
    return 1;
  }

  /* Make sure we have a valid query engine.  If not, create a new one.
  */
  v = sqliteGetVdbe(pParse);
  if( v==0 ) return 1;

  /* Create the destination temporary table if necessary
  */
  if( eDest==SRT_TempTable ){
    sqliteVdbeAddOp(v, OP_OpenTemp, iParm, 0);
    eDest = SRT_Table;
  }

  /* Process the UNION or INTERSECTION
  */
  base = pParse->nTab;
  switch( p->op ){
    case TK_ALL:
    case TK_EXCEPT:
    case TK_UNION: {
      int unionTab;    /* Cursor number of the temporary table holding result */
      int op;          /* One of the SRT_ operations to apply to self */
      int priorOp;     /* The SRT_ operation to apply to prior selects */

      priorOp = p->op==TK_ALL ? SRT_Table : SRT_Union;
      if( eDest==priorOp ){
        /* We can reuse a temporary table generated by a SELECT to our
        ** right.  This also means we are not the right-most select and so
        ** we cannot have an ORDER BY clause
        */
        unionTab = iParm;
        assert( p->pOrderBy==0 );
      }else{
        /* We will need to create our own temporary table to hold the
        ** intermediate results.
        */
        unionTab = pParse->nTab++;
        if( p->pOrderBy 
        && matchOrderbyToColumn(pParse, p, p->pOrderBy, unionTab, 1) ){
          return 1;
        }
        if( p->op!=TK_ALL ){
          sqliteVdbeAddOp(v, OP_OpenTemp, unionTab, 1);
          sqliteVdbeAddOp(v, OP_KeyAsData, unionTab, 1);
        }else{
          sqliteVdbeAddOp(v, OP_OpenTemp, unionTab, 0);
        }
      }

      /* Code the SELECT statements to our left
      */
      rc = sqliteSelect(pParse, pPrior, priorOp, unionTab, 0, 0, 0);
      if( rc ) return rc;

      /* Code the current SELECT statement
      */
      switch( p->op ){
         case TK_EXCEPT:  op = SRT_Except;   break;
         case TK_UNION:   op = SRT_Union;    break;
         case TK_ALL:     op = SRT_Table;    break;
      }
      p->pPrior = 0;
      rc = sqliteSelect(pParse, p, op, unionTab, 0, 0, 0);
      p->pPrior = pPrior;
      if( rc ) return rc;

      /* Convert the data in the temporary table into whatever form
      ** it is that we currently need.
      */      
      if( eDest!=priorOp ){
        int iCont, iBreak, iStart;
        assert( p->pEList );
        if( eDest==SRT_Callback ){
          generateColumnNames(pParse, p->base, 0, p->pEList);
        }
        iBreak = sqliteVdbeMakeLabel(v);
        iCont = sqliteVdbeMakeLabel(v);
        sqliteVdbeAddOp(v, OP_Rewind, unionTab, iBreak);
        iStart = sqliteVdbeCurrentAddr(v);
        rc = selectInnerLoop(pParse, 0, unionTab, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak);
        if( rc ) return 1;
        sqliteVdbeResolveLabel(v, iCont);
        sqliteVdbeAddOp(v, OP_Next, unionTab, iStart);
        sqliteVdbeResolveLabel(v, iBreak);
        sqliteVdbeAddOp(v, OP_Close, unionTab, 0);
        if( p->pOrderBy ){
          generateSortTail(v, p->pEList->nExpr);
        }
      }
      break;
    }
    case TK_INTERSECT: {
      int tab1, tab2;
      int iCont, iBreak, iStart;

      /* 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++;
      if( p->pOrderBy && matchOrderbyToColumn(pParse,p,p->pOrderBy,tab1,1) ){
        return 1;
      }
      sqliteVdbeAddOp(v, OP_OpenTemp, tab1, 1);
      sqliteVdbeAddOp(v, OP_KeyAsData, tab1, 1);

      /* Code the SELECTs to our left into temporary table "tab1".
      */
      rc = sqliteSelect(pParse, pPrior, SRT_Union, tab1, 0, 0, 0);
      if( rc ) return rc;

      /* Code the current SELECT into temporary table "tab2"
      */
      sqliteVdbeAddOp(v, OP_OpenTemp, tab2, 1);
      sqliteVdbeAddOp(v, OP_KeyAsData, tab2, 1);
      p->pPrior = 0;
      rc = sqliteSelect(pParse, p, SRT_Union, tab2, 0, 0, 0);
      p->pPrior = pPrior;
      if( rc ) return rc;

      /* Generate code to take the intersection of the two temporary
      ** tables.
      */
      assert( p->pEList );
      if( eDest==SRT_Callback ){
        generateColumnNames(pParse, p->base, 0, p->pEList);
      }
      iBreak = sqliteVdbeMakeLabel(v);
      iCont = sqliteVdbeMakeLabel(v);
      sqliteVdbeAddOp(v, OP_Rewind, tab1, iBreak);
      iStart = sqliteVdbeAddOp(v, OP_FullKey, tab1, 0);
      sqliteVdbeAddOp(v, OP_NotFound, tab2, iCont);
      rc = selectInnerLoop(pParse, 0, tab1, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak);
      if( rc ) return 1;
      sqliteVdbeResolveLabel(v, iCont);
      sqliteVdbeAddOp(v, OP_Next, tab1, iStart);
      sqliteVdbeResolveLabel(v, iBreak);
      sqliteVdbeAddOp(v, OP_Close, tab2, 0);
      sqliteVdbeAddOp(v, OP_Close, tab1, 0);
      if( p->pOrderBy ){
        generateSortTail(v, p->pEList->nExpr);
      }
      break;
    }
  }
  assert( p->pEList && pPrior->pEList );
  if( p->pEList->nExpr!=pPrior->pEList->nExpr ){
    sqliteSetString(&pParse->zErrMsg, "SELECTs to the left and right of ",
      selectOpName(p->op), " do not have the same number of result columns", 0);
    pParse->nErr++;
    return 1;
  }
  pParse->nTab = base;
  return 0;
}

/*
** Recursively scan through an expression tree.  For every reference
** to a column in table number iFrom, change that reference to the
** same column in table number iTo.
*/
static void changeTables(Expr *pExpr, int iFrom, int iTo){
  if( pExpr==0 ) return;
  if( pExpr->op==TK_COLUMN && pExpr->iTable==iFrom ){
    pExpr->iTable = iTo;
  }else{
    static void changeTablesInList(ExprList*, int, int);
    changeTables(pExpr->pLeft, iFrom, iTo);
    changeTables(pExpr->pRight, iFrom, iTo);
    changeTablesInList(pExpr->pList, iFrom, iTo);
  }
}
static void changeTablesInList(ExprList *pList, int iFrom, int iTo){
  if( pList ){
    int i;
    for(i=0; i<pList->nExpr; i++){
      changeTables(pList->a[i].pExpr, iFrom, iTo);
    }
  }
}

/*
** Scan through the expression pExpr.  Replace every reference to
** a column in table number iTable with a copy of the corresponding
** entry in pEList.  (But leave references to the ROWID column 
** unchanged.)  When making a copy of an expression in pEList, change
** references to columns in table iSub into references to table iTable.
**
** 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(Expr *pExpr, int iTable, ExprList *pEList, int iSub){
  if( pExpr==0 ) return;
  if( pExpr->op==TK_COLUMN && pExpr->iTable==iTable && pExpr->iColumn>=0 ){
    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;
    pExpr->pLeft = sqliteExprDup(pNew->pLeft);
    pExpr->pRight = sqliteExprDup(pNew->pRight);
    pExpr->pList = sqliteExprListDup(pNew->pList);
    pExpr->iTable = pNew->iTable;
    pExpr->iColumn = pNew->iColumn;
    pExpr->iAgg = pNew->iAgg;
    pExpr->token = pNew->token;
    if( iSub!=iTable ){
      changeTables(pExpr, iSub, iTable);
    }
  }else{
    static void substExprList(ExprList*,int,ExprList*,int);
    substExpr(pExpr->pLeft, iTable, pEList, iSub);
    substExpr(pExpr->pRight, iTable, pEList, iSub);
    substExprList(pExpr->pList, iTable, pEList, iSub);
  }
}
static void 
substExprList(ExprList *pList, int iTable, ExprList *pEList, int iSub){
  int i;
  if( pList==0 ) return;
  for(i=0; i<pList->nExpr; i++){
    substExpr(pList->a[i].pExpr, iTable, pEList, iSub);
  }
}

/*
** 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 a join.
**
**   (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.
**
** 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 return 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.
*/
int flattenSubquery(Select *p, int iFrom, int isAgg, int subqueryIsAgg){
  Select *pSub;       /* The inner query or "subquery" */
  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 i;
  int iParent, iSub;
  Expr *pWhere;

  /* 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 );
  pSub = pSrc->a[iFrom].pSelect;
  assert( pSub!=0 );
  if( isAgg && subqueryIsAgg ) return 0;
  if( subqueryIsAgg && pSrc->nSrc>1 ) return 0;
  pSubSrc = pSub->pSrc;
  assert( pSubSrc );
  if( pSubSrc->nSrc!=1 ) return 0;
  if( pSub->isDistinct && pSrc->nSrc>1 ) return 0;
  if( pSub->isDistinct && isAgg ) return 0;
  if( p->isDistinct && subqueryIsAgg ) return 0;

  /* If we reach this point, it means flattening is permitted for the
  ** i-th entry of the FROM clause in the outer query.
  */
  iParent = p->base + iFrom;
  iSub = pSub->base;
  substExprList(p->pEList, iParent, pSub->pEList, iSub);
  pList = p->pEList;
  for(i=0; i<pList->nExpr; i++){
    if( pList->a[i].zName==0 ){
      Expr *pExpr = pList->a[i].pExpr;
      pList->a[i].zName = sqliteStrNDup(pExpr->span.z, pExpr->span.n);
    }
  }
  if( isAgg ){
    substExprList(p->pGroupBy, iParent, pSub->pEList, iSub);
    substExpr(p->pHaving, iParent, pSub->pEList, iSub);
  }
  substExprList(p->pOrderBy, iParent, pSub->pEList, iSub);
  if( pSub->pWhere ){
    pWhere = sqliteExprDup(pSub->pWhere);
    if( iParent!=iSub ){
      changeTables(pWhere, iSub, iParent);
    }
  }else{
    pWhere = 0;
  }
  if( subqueryIsAgg ){
    assert( p->pHaving==0 );
    p->pHaving = p->pWhere;
    p->pWhere = pWhere;
    substExpr(p->pHaving, iParent, pSub->pEList, iSub);
    if( pSub->pHaving ){
      Expr *pHaving = sqliteExprDup(pSub->pHaving);
      if( iParent!=iSub ){
        changeTables(pHaving, iSub, iParent);
      }
      if( p->pHaving ){
        p->pHaving = sqliteExpr(TK_AND, p->pHaving, pHaving, 0);
      }else{
        p->pHaving = pHaving;
      }
    }
    assert( p->pGroupBy==0 );
    p->pGroupBy = sqliteExprListDup(pSub->pGroupBy);
    if( iParent!=iSub ){
      changeTablesInList(p->pGroupBy, iSub, iParent);
    }
  }else if( p->pWhere==0 ){
    p->pWhere = pWhere;
  }else{
    substExpr(p->pWhere, iParent, pSub->pEList, iSub);
    if( pWhere ){
      p->pWhere = sqliteExpr(TK_AND, p->pWhere, pWhere, 0);
    }
  }
  p->isDistinct = p->isDistinct || pSub->isDistinct;
  if( pSrc->a[iFrom].pTab && pSrc->a[iFrom].pTab->isTransient ){
    sqliteDeleteTable(0, pSrc->a[iFrom].pTab);
  }
  pSrc->a[iFrom].pTab = pSubSrc->a[0].pTab;
  pSubSrc->a[0].pTab = 0;
  pSrc->a[iFrom].pSelect = pSubSrc->a[0].pSelect;
  pSubSrc->a[0].pSelect = 0;
  sqliteSelectDelete(pSub);
  return 1;
}

/*
** Analyze the SELECT statement passed in as an argument to see if it
** is a simple min() or max() query.  If it is and this query can be
** satisfied using a single seek to the beginning or end of an index,
** then generate the code for this SELECT return 1.  If this is not a 
** simple min() or max() query, then return 0;
**
** A simply min() or max() query looks like this:
**
**    SELECT min(a) FROM table;
**    SELECT max(a) FROM table;
**
** The query may have only a single table in its FROM argument.  There
** can be no GROUP BY or HAVING or WHERE clauses.  The result set must
** be the min() or max() of a single column of the table.  The column
** in the min() or max() function must be indexed.
**
** The parameters to this routine are the same as for sqliteSelect().
** See the header comment on that routine for additional information.
*/
static int simpleMinMaxQuery(Parse *pParse, Select *p, int eDest, int iParm){
  Expr *pExpr;
  int iCol;
  Table *pTab;
  Index *pIdx;
  int base;
  Vdbe *v;
  int openOp;
  int seekOp;
  int cont;
  ExprList eList;
  struct ExprList_item eListItem;

  /* Check to see if this query is a simple min() or max() query.  Return
  ** zero if it is  not.
  */
  if( p->pGroupBy || p->pHaving || p->pWhere ) return 0;
  if( p->pSrc->nSrc!=1 ) return 0;
  if( p->pEList->nExpr!=1 ) return 0;
  pExpr = p->pEList->a[0].pExpr;
  if( pExpr->op!=TK_AGG_FUNCTION ) return 0;
  if( pExpr->pList==0 || pExpr->pList->nExpr!=1 ) return 0;
  if( pExpr->token.n!=3 ) return 0;
  if( sqliteStrNICmp(pExpr->token.z,"min",3)==0 ){
    seekOp = OP_Rewind;
  }else if( sqliteStrNICmp(pExpr->token.z,"max",3)==0 ){
    seekOp = OP_Last;
  }else{
    return 0;
  }
  pExpr = pExpr->pList->a[0].pExpr;
  if( pExpr->op!=TK_COLUMN ) return 0;
  iCol = pExpr->iColumn;
  pTab = p->pSrc->a[0].pTab;

  /* If we get to here, it means the query is of the correct form.
  ** Check to make sure we have an index and make pIdx point to the
  ** appropriate index.  If the min() or max() is on an INTEGER PRIMARY
  ** key column, no index is necessary so set pIdx to NULL.  If no
  ** usable index is found, return 0.
  */
  if( iCol<0 ){
    pIdx = 0;
  }else{
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
      assert( pIdx->nColumn>=1 );
      if( pIdx->aiColumn[0]==iCol ) break;
    }
    if( pIdx==0 ) return 0;
  }

  /* Identify column names if we will be using the callback.  This
  ** step is skipped if the output is going to a table or a memory cell.
  */
  v = sqliteGetVdbe(pParse);
  if( v==0 ) return 0;
  if( eDest==SRT_Callback ){
    generateColumnNames(pParse, p->base, p->pSrc, p->pEList);
  }

  /* Generating code to find the min or the max.  Basically all we have
  ** to do is find the first or the last entry in the chosen index.  If
  ** the min() or max() is on the INTEGER PRIMARY KEY, then find the first
  ** or last entry in the main table.
  */
  if( !pParse->schemaVerified && (pParse->db->flags & SQLITE_InTrans)==0 ){
    sqliteVdbeAddOp(v, OP_VerifyCookie, pParse->db->schema_cookie, 0);
    pParse->schemaVerified = 1;
  }
  openOp = pTab->isTemp ? OP_OpenAux : OP_Open;
  base = p->base;
  sqliteVdbeAddOp(v, openOp, base, pTab->tnum);
  sqliteVdbeChangeP3(v, -1, pTab->zName, P3_STATIC);
  if( pIdx==0 ){
    sqliteVdbeAddOp(v, seekOp, base, 0);
  }else{
    sqliteVdbeAddOp(v, openOp, base+1, pIdx->tnum);
    sqliteVdbeChangeP3(v, -1, pIdx->zName, P3_STATIC);
    sqliteVdbeAddOp(v, seekOp, base+1, 0);
    sqliteVdbeAddOp(v, OP_IdxRecno, base+1, 0);
    sqliteVdbeAddOp(v, OP_Close, base+1, 0);
    sqliteVdbeAddOp(v, OP_MoveTo, base, 0);
  }
  eList.nExpr = 1;
  memset(&eListItem, 0, sizeof(eListItem));
  eList.a = &eListItem;
  eList.a[0].pExpr = pExpr;
  cont = sqliteVdbeMakeLabel(v);
  selectInnerLoop(pParse, &eList, base, 1, 0, -1, eDest, iParm, cont, cont);
  sqliteVdbeResolveLabel(v, cont);
  sqliteVdbeAddOp(v, OP_Close, base, 0);
  return 1;
}

/*
** Generate code for the given SELECT statement.
**
** The results are distributed in various ways depending on the
** value of eDest and iParm.
**
**     eDest Value       Result
**     ------------    -------------------------------------------
**     SRT_Callback    Invoke the callback for each row of the result.
**
**     SRT_Mem         Store first result in memory cell iParm
**
**     SRT_Set         Store results as keys of a table with cursor iParm
**
**     SRT_Union       Store results as a key in a temporary table iParm
**
**     SRT_Except      Remove results form the temporary table iParm.
**
**     SRT_Table       Store results in temporary table iParm
**
** This routine returns the number of errors.  If any errors are
** encountered, then an appropriate error message is left in
** pParse->zErrMsg.
**
** This routine does NOT free the Select structure passed in.  The
** calling function needs to do that.
**
** The pParent, parentTab, and *pParentAgg fields are filled in if this
** SELECT is a subquery.  This routine may try to combine this SELECT
** with its parent to form a single flat query.  In so doing, it might
** change the parent query from a non-aggregate to an aggregate query.
** For that reason, the pParentAgg flag is passed as a pointer, so it
** can be changed.
*/
int sqliteSelect(
  Parse *pParse,         /* The parser context */
  Select *p,             /* The SELECT statement being coded. */
  int eDest,             /* One of: SRT_Callback Mem Set Union Except */
  int iParm,             /* Save result in this memory location, if >=0 */
  Select *pParent,       /* Another SELECT for which this is a sub-query */
  int parentTab,         /* Index in pParent->pSrc of this query */
  int *pParentAgg        /* True if pParent uses aggregate functions */
){
  int i;
  WhereInfo *pWInfo;
  Vdbe *v;
  int isAgg = 0;         /* True for select lists like "count(*)" */
  ExprList *pEList;      /* List of columns to extract. */
  SrcList *pTabList;     /* List of tables to select from */
  Expr *pWhere;          /* The WHERE clause.  May be NULL */
  ExprList *pOrderBy;    /* The ORDER BY clause.  May be NULL */
  ExprList *pGroupBy;    /* The GROUP BY clause.  May be NULL */
  Expr *pHaving;         /* The HAVING clause.  May be NULL */
  int isDistinct;        /* True if the DISTINCT keyword is present */
  int distinct;          /* Table to use for the distinct set */
  int base;              /* First cursor available for use */
  int rc = 1;            /* Value to return from this function */

  if( sqlite_malloc_failed || pParse->nErr || p==0 ) return 1;

  /* If there is are a sequence of queries, do the earlier ones first.
  */
  if( p->pPrior ){
    return multiSelect(pParse, p, eDest, iParm);
  }

  /* Make local copies of the parameters for this query.
  */
  pTabList = p->pSrc;
  pWhere = p->pWhere;
  pOrderBy = p->pOrderBy;
  pGroupBy = p->pGroupBy;
  pHaving = p->pHaving;
  isDistinct = p->isDistinct;

  /* Allocate a block of VDBE cursors, one for each table in the FROM clause.
  ** The WHERE processing requires that the cursors for the tables in the
  ** FROM clause be consecutive.
  */
  base = p->base = pParse->nTab;
  pParse->nTab += pTabList->nSrc;

  /* 
  ** Do not even attempt to generate any code if we have already seen
  ** errors before this routine starts.
  */
  if( pParse->nErr>0 ) goto select_end;

  /* Look up every table in the table list and create an appropriate
  ** columnlist in pEList if there isn't one already.  (The parser leaves
  ** a NULL in the p->pEList if the SQL said "SELECT * FROM ...")
  */
  if( fillInColumnList(pParse, p) ){
    goto select_end;
  }
  pWhere = p->pWhere;
  pEList = p->pEList;
  if( pEList==0 ) goto select_end;

  /* If writing to memory or generating a set
  ** only a single column may be output.
  */
  if( (eDest==SRT_Mem || eDest==SRT_Set) && pEList->nExpr>1 ){
    sqliteSetString(&pParse->zErrMsg, "only a single result allowed for "
       "a SELECT that is part of an expression", 0);
    pParse->nErr++;
    goto select_end;
  }

  /* ORDER BY is ignored if we are not sending the result to a callback.
  */
  if( eDest!=SRT_Callback ){
    pOrderBy = 0;
  }

  /* At this point, we should have allocated all the cursors that we
  ** need to handle subquerys and temporary tables.  
  **
  ** Resolve the column names and do a semantics check on all the expressions.
  */
  for(i=0; i<pEList->nExpr; i++){
    if( sqliteExprResolveIds(pParse, base, pTabList, 0, pEList->a[i].pExpr) ){
      goto select_end;
    }
    if( sqliteExprCheck(pParse, pEList->a[i].pExpr, 1, &isAgg) ){
      goto select_end;
    }
  }
  if( pWhere ){
    if( sqliteExprResolveIds(pParse, base, pTabList, pEList, pWhere) ){
      goto select_end;
    }
    if( sqliteExprCheck(pParse, pWhere, 0, 0) ){
      goto select_end;
    }
  }
  if( pOrderBy ){
    for(i=0; i<pOrderBy->nExpr; i++){
      Expr *pE = pOrderBy->a[i].pExpr;
      if( sqliteExprIsConstant(pE) ){
        sqliteSetString(&pParse->zErrMsg, 
             "ORDER BY expressions should not be constant", 0);
        pParse->nErr++;
        goto select_end;
      }
      if( sqliteExprResolveIds(pParse, base, pTabList, pEList, pE) ){
        goto select_end;
      }
      if( sqliteExprCheck(pParse, pE, isAgg, 0) ){
        goto select_end;
      }
    }
  }
  if( pGroupBy ){
    for(i=0; i<pGroupBy->nExpr; i++){
      Expr *pE = pGroupBy->a[i].pExpr;
      if( sqliteExprIsConstant(pE) ){
        sqliteSetString(&pParse->zErrMsg, 
             "GROUP BY expressions should not be constant", 0);
        pParse->nErr++;
        goto select_end;
      }
      if( sqliteExprResolveIds(pParse, base, pTabList, pEList, pE) ){
        goto select_end;
      }
      if( sqliteExprCheck(pParse, pE, isAgg, 0) ){
        goto select_end;
      }
    }
  }
  if( pHaving ){
    if( pGroupBy==0 ){
      sqliteSetString(&pParse->zErrMsg, "a GROUP BY clause is required "
         "before HAVING", 0);
      pParse->nErr++;
      goto select_end;
    }
    if( sqliteExprResolveIds(pParse, base, pTabList, pEList, pHaving) ){
      goto select_end;
    }
    if( sqliteExprCheck(pParse, pHaving, isAgg, 0) ){
      goto select_end;
    }
  }

  /* Check for the special case of a min() or max() function by itself
  ** in the result set.
  */
  if( simpleMinMaxQuery(pParse, p, eDest, iParm) ){
    rc = 0;
    goto select_end;
  }

  /* Begin generating code.
  */
  v = sqliteGetVdbe(pParse);
  if( v==0 ) goto select_end;

  /* Identify column names if we will be using in the callback.  This
  ** step is skipped if the output is going to a table or a memory cell.
  */
  if( eDest==SRT_Callback ){
    generateColumnNames(pParse, p->base, pTabList, pEList);
  }

  /* Set the limiter
  */
  if( p->nLimit<=0 ){
    p->nOffset = 0;
  }else{
    if( p->nOffset<0 ) p->nOffset = 0;
    sqliteVdbeAddOp(v, OP_Limit, p->nLimit, p->nOffset);
  }

  /* Generate code for all sub-queries in the FROM clause
  */
  for(i=0; i<pTabList->nSrc; i++){
    if( pTabList->a[i].pSelect==0 ) continue;
    sqliteSelect(pParse, pTabList->a[i].pSelect, SRT_TempTable, base+i,
                 p, i, &isAgg);
    pTabList = p->pSrc;
    pWhere = p->pWhere;
    if( eDest==SRT_Callback ){
      pOrderBy = p->pOrderBy;
    }
    pGroupBy = p->pGroupBy;
    pHaving = p->pHaving;
    isDistinct = p->isDistinct;
  }

  /* Check to see if this is a subquery that can be "flattened" into its parent.
  ** If flattening is a possiblity, do so and return immediately.  
  */
  if( pParent && pParentAgg &&
      flattenSubquery(pParent, parentTab, *pParentAgg, isAgg) ){
    if( isAgg ) *pParentAgg = 1;
    return rc;
  }

  /* If the output is destined for a temporary table, open that table.
  */
  if( eDest==SRT_TempTable ){
    sqliteVdbeAddOp(v, OP_OpenTemp, iParm, 0);
  }

  /* Do an analysis of aggregate expressions.
  */
  sqliteAggregateInfoReset(pParse);
  if( isAgg ){
    assert( pParse->nAgg==0 );
    for(i=0; i<pEList->nExpr; i++){
      if( sqliteExprAnalyzeAggregates(pParse, pEList->a[i].pExpr) ){
        goto select_end;
      }
    }
    if( pGroupBy ){
      for(i=0; i<pGroupBy->nExpr; i++){
        if( sqliteExprAnalyzeAggregates(pParse, pGroupBy->a[i].pExpr) ){
          goto select_end;
        }
      }
    }
    if( pHaving && sqliteExprAnalyzeAggregates(pParse, pHaving) ){
      goto select_end;
    }
    if( pOrderBy ){
      for(i=0; i<pOrderBy->nExpr; i++){
        if( sqliteExprAnalyzeAggregates(pParse, pOrderBy->a[i].pExpr) ){
          goto select_end;
        }
      }
    }
  }

  /* Reset the aggregator
  */
  if( isAgg ){
    sqliteVdbeAddOp(v, OP_AggReset, 0, pParse->nAgg);
    for(i=0; i<pParse->nAgg; i++){
      FuncDef *pFunc;
      if( (pFunc = pParse->aAgg[i].pFunc)!=0 && pFunc->xFinalize!=0 ){
        sqliteVdbeAddOp(v, OP_AggInit, 0, i);
        sqliteVdbeChangeP3(v, -1, (char*)pFunc, P3_POINTER);
      }
    }
    if( pGroupBy==0 ){
      sqliteVdbeAddOp(v, OP_String, 0, 0);
      sqliteVdbeAddOp(v, OP_AggFocus, 0, 0);
    }
  }

  /* Initialize the memory cell to NULL
  */
  if( eDest==SRT_Mem ){
    sqliteVdbeAddOp(v, OP_String, 0, 0);
    sqliteVdbeAddOp(v, OP_MemStore, iParm, 1);
  }

  /* Open a temporary table to use for the distinct set.
  */
  if( isDistinct ){
    distinct = pParse->nTab++;
    sqliteVdbeAddOp(v, OP_OpenTemp, distinct, 1);
  }else{
    distinct = -1;
  }

  /* Begin the database scan
  */
  pWInfo = sqliteWhereBegin(pParse, p->base, pTabList, pWhere, 0);
  if( pWInfo==0 ) goto select_end;

  /* Use the standard inner loop if we are not dealing with
  ** aggregates
  */
  if( !isAgg ){
    if( selectInnerLoop(pParse, pEList, 0, 0, pOrderBy, distinct, eDest, iParm,
                    pWInfo->iContinue, pWInfo->iBreak) ){
       goto select_end;
    }
  }

  /* If we are dealing with aggregates, then to the special aggregate
  ** processing.  
  */
  else{
    if( pGroupBy ){
      int lbl1;
      for(i=0; i<pGroupBy->nExpr; i++){
        sqliteExprCode(pParse, pGroupBy->a[i].pExpr);
      }
      sqliteVdbeAddOp(v, OP_MakeKey, pGroupBy->nExpr, 0);
      lbl1 = sqliteVdbeMakeLabel(v);
      sqliteVdbeAddOp(v, OP_AggFocus, 0, lbl1);
      for(i=0; i<pParse->nAgg; i++){
        if( pParse->aAgg[i].isAgg ) continue;
        sqliteExprCode(pParse, pParse->aAgg[i].pExpr);
        sqliteVdbeAddOp(v, OP_AggSet, 0, i);
      }
      sqliteVdbeResolveLabel(v, lbl1);
    }
    for(i=0; i<pParse->nAgg; i++){
      Expr *pE;
      int j;
      if( !pParse->aAgg[i].isAgg ) continue;
      pE = pParse->aAgg[i].pExpr;
      assert( pE->op==TK_AGG_FUNCTION );
      if( pE->pList ){
        for(j=0; j<pE->pList->nExpr; j++){
          sqliteExprCode(pParse, pE->pList->a[j].pExpr);
        }
      }
      sqliteVdbeAddOp(v, OP_Integer, i, 0);
      sqliteVdbeAddOp(v, OP_AggFunc, 0, pE->pList ? pE->pList->nExpr : 0);
      assert( pParse->aAgg[i].pFunc!=0 );
      assert( pParse->aAgg[i].pFunc->xStep!=0 );
      sqliteVdbeChangeP3(v, -1, (char*)pParse->aAgg[i].pFunc, P3_POINTER);
    }
  }

  /* End the database scan loop.
  */
  sqliteWhereEnd(pWInfo);

  /* If we are processing aggregates, we need to set up a second loop
  ** over all of the aggregate values and process them.
  */
  if( isAgg ){
    int endagg = sqliteVdbeMakeLabel(v);
    int startagg;
    startagg = sqliteVdbeAddOp(v, OP_AggNext, 0, endagg);
    pParse->useAgg = 1;
    if( pHaving ){
      sqliteExprIfFalse(pParse, pHaving, startagg);
    }
    if( selectInnerLoop(pParse, pEList, 0, 0, pOrderBy, distinct, eDest, iParm,
                    startagg, endagg) ){
      goto select_end;
    }
    sqliteVdbeAddOp(v, OP_Goto, 0, startagg);
    sqliteVdbeResolveLabel(v, endagg);
    sqliteVdbeAddOp(v, OP_Noop, 0, 0);
    pParse->useAgg = 0;
  }

  /* If there is an ORDER BY clause, then we need to sort the results
  ** and send them to the callback one by one.
  */
  if( pOrderBy ){
    generateSortTail(v, pEList->nExpr);
  }


  /* Issue a null callback if that is what the user wants.
  */
  if( (pParse->db->flags & SQLITE_NullCallback)!=0 && eDest==SRT_Callback ){
    sqliteVdbeAddOp(v, OP_NullCallback, pEList->nExpr, 0);
  }

  /* The SELECT was successfully coded.   Set the return code to 0
  ** to indicate no errors.
  */
  rc = 0;

  /* Control jumps to here if an error is encountered above, or upon
  ** successful coding of the SELECT.
  */
select_end:
  pParse->nTab = base;
  sqliteAggregateInfoReset(pParse);
  return rc;
}