SQLite

**   drh@hwaci.com
**   http://www.hwaci.com/drh/
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements.
**
** $Id: select.c,v 1.17 2000/06/08 00:19:03 drh Exp $
*/
#include "sqliteInt.h"

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

    

/*
** 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.
  */
  assert( p->pPrior!=0 );
  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;

  /* 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 */

  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;
}

/*
** Generate code for the given SELECT statement.
**
** The results are distributed in various ways depending on the

  IdList *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 */

  /* 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;

  /* Save the current value of pParse->nTab.  Restore this value before
  ** we exit.
  */
  base = pParse->nTab;

  /* 
  ** Do not even attempt to generate any code if we have already seen
  ** errors before this routine starts.
  */
  if( pParse->nErr>0 ) return 1;
  sqliteParseInfoReset(pParse);

  /* 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 pEList field if the SQL said "SELECT * FROM ...")
  */
  if( fillInColumnList(pParse, p) ){

  if( pGroupBy ){
    for(i=0; i<pGroupBy->nExpr; i++){
      sqliteExprResolveInSelect(pParse, pGroupBy->a[i].pExpr);
    }
  }
  if( pHaving ) sqliteExprResolveInSelect(pParse, pHaving);

  /* At this point, we should have allocated all the cursors that we
  ** need to handle subquerys and temporary tables.  From here on we
  ** are committed to keeping the same value for pParse->nTab.
  **
  ** Resolve the field names and do a semantics check on all the expressions.
  */
  for(i=0; i<pEList->nExpr; i++){
    if( sqliteExprResolveIds(pParse, pTabList, pEList->a[i].pExpr) ){
      return 1;
    }
    if( sqliteExprCheck(pParse, pEList->a[i].pExpr, 1, &isAgg) ){
      return 1;

  /* 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);
  }
  pParse->nTab = base;
  return 0;
}