SQLite

**    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 1.517 2009/05/18 15:46:08 drh Exp $
*/
#include "sqliteInt.h"


/*
** Delete all the content of a Select structure but do not deallocate
** the select structure itself.

        pDest->nMem = pIn->nMem;
      }
      sqlite3ExprCodeMove(pParse, pIn->iMem, pDest->iMem, pDest->nMem);
      sqlite3VdbeAddOp1(v, OP_Yield, pDest->iParm);
      break;
    }

    /* If none of the above, then the result destination must be
    ** SRT_Output.  This routine is never called with any other
    ** destination other than the ones handled above or SRT_Output.
    **
    ** For SRT_Output, 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.
    */
    default: {
      assert( pDest->eDest==SRT_Output );
      sqlite3VdbeAddOp2(v, OP_ResultRow, pIn->iMem, pIn->nMem);
      sqlite3ExprCacheAffinityChange(pParse, pIn->iMem, pIn->nMem);
      break;
    }











  }

  /* 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);

  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;
  assert( v!=0 );       /* Already thrown the error if VDBE alloc failed */
  labelEnd = sqlite3VdbeMakeLabel(v);
  labelCmpr = sqlite3VdbeMakeLabel(v);


  /* Patch up the ORDER BY clause
  */
  op = p->op;  

    if( pSub->pOrderBy ){
      return 0;  /* Restriction 20 */
    }
    if( isAgg || (p->selFlags & SF_Distinct)!=0 || pSrc->nSrc!=1 ){
      return 0;
    }
    for(pSub1=pSub; pSub1; pSub1=pSub1->pPrior){
      testcase( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct );
      testcase( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))==SF_Aggregate );
      if( (pSub1->selFlags & (SF_Distinct|SF_Aggregate))!=0
       || (pSub1->pPrior && pSub1->op!=TK_ALL) 
       || NEVER(pSub1->pSrc==0) || pSub1->pSrc->nSrc!=1
      ){
        return 0;
      }
    }

    /* Restriction 18. */
    if( p->pOrderBy ){

  pSubitem->zAlias = 0;
  pSubitem->pSelect = 0;

  /* Defer deleting the Table object associated with the
  ** subquery until code generation is
  ** complete, since there may still exist Expr.pTab entries that
  ** refer to the subquery even after flattening.  Ticket #3346.
  **
  ** pSubitem->pTab is always non-NULL by test restrictions and tests above.
  */
  if( ALWAYS(pSubitem->pTab!=0) ){
    Table *pTabToDel = pSubitem->pTab;
    if( pTabToDel->nRef==1 ){
      pTabToDel->pNextZombie = pParse->pZombieTab;
      pParse->pZombieTab = pTabToDel;
    }else{
      pTabToDel->nRef--;
    }

    **    \_____________________ outer query ______________________________/
    **
    ** We look at every expression in the outer query and every place we see
    ** "a" we substitute "x*3" and every place we see "b" we substitute "y+10".
    */
    pList = pParent->pEList;
    for(i=0; i<pList->nExpr; i++){
      if( pList->a[i].zName==0 ){
        Expr *pExpr = pList->a[i].pExpr;
        if( ALWAYS(pExpr->span.z!=0) ){
          pList->a[i].zName = 
               sqlite3DbStrNDup(db, (char*)pExpr->span.z, pExpr->span.n);
        }
      }
    }
    substExprList(db, pParent->pEList, iParent, pSub->pEList);
    if( isAgg ){
      substExprList(db, pParent->pGroupBy, iParent, pSub->pEList);
      substExpr(db, pParent->pHaving, iParent, pSub->pEList);
    }

  db = pParse->db;
  if( p==0 || db->mallocFailed || pParse->nErr ){
    return 1;
  }
  if( sqlite3AuthCheck(pParse, SQLITE_SELECT, 0, 0, 0) ) return 1;
  memset(&sAggInfo, 0, sizeof(sAggInfo));


  if( IgnorableOrderby(pDest) ){





    assert(pDest->eDest==SRT_Exists || pDest->eDest==SRT_Union || 
           pDest->eDest==SRT_Except || pDest->eDest==SRT_Discard);
    /* If ORDER BY makes no difference in the output then neither does
    ** DISTINCT so it can be removed too. */
    sqlite3ExprListDelete(db, p->pOrderBy);
    p->pOrderBy = 0;
    p->selFlags &= ~SF_Distinct;
  }
  sqlite3SelectPrep(pParse, p, 0);
  pOrderBy = p->pOrderBy;
  pTabList = p->pSrc;
  pEList = p->pEList;
  if( pParse->nErr || db->mallocFailed ){
    goto select_end;
  }
  isAgg = (p->selFlags & SF_Aggregate)!=0;
  if( pEList==0 ) goto select_end;

  /* 
  ** 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;







  /* Begin generating code.
  */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ) goto select_end;

  /* Generate code for all sub-queries in the FROM clause
  */