SQLite

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 distinctTab,        /* 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->iSDParm; /* First argument to disposal method */
  int nResultCol;             /* Number of result columns */

  assert( v );
  if( NEVER(v==0) ) return;
  assert( pEList!=0 );
  hasDistinct = distinctTab>=0;
  if( pOrderBy==0 && !hasDistinct ){
    codeOffset(v, p, iContinue);
  }

  /* Pull the requested columns.
  */
  if( nColumn>0 ){

  /* 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, distinctTab, iContinue, nColumn, regResult);
    if( pOrderBy==0 ){
      codeOffset(v, p, iContinue);
    }
  }

  switch( eDest ){
    /* In this mode, write each query result to the key of the temporary

  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 distinctTab;       /* Table to use for the distinct set */
  int rc = 1;            /* Value to return from this function */
  int addrSortIndex;     /* Address of an OP_OpenEphemeral instruction */
  int addrDistinctIndex; /* Address of an OP_OpenEphemeral instruction */
  AggInfo sAggInfo;      /* Information used by aggregate queries */
  int iEnd;              /* Address of the end of the query */
  sqlite3 *db;           /* The database connection */

    p->selFlags |= SF_UseSorter;
  }

  /* Open a virtual index to use for the distinct set.
  */
  if( p->selFlags & SF_Distinct ){
    KeyInfo *pKeyInfo;
    distinctTab = pParse->nTab++;
    pKeyInfo = keyInfoFromExprList(pParse, p->pEList);
    addrDistinctIndex = sqlite3VdbeAddOp4(v, OP_OpenEphemeral, distinctTab,
                                   0, 0, (char*)pKeyInfo, P4_KEYINFO_HANDOFF);
    sqlite3VdbeChangeP5(v, BTREE_UNORDERED);
  }else{
    distinctTab = addrDistinctIndex = -1;
  }

  /* Aggregate and non-aggregate queries are handled differently */
  if( !isAgg && pGroupBy==0 ){
    ExprList *pDist = (isDistinct ? p->pEList : 0);

    /* Begin the database scan. */

      p->addrOpenEphm[2] = -1;
    }

    if( pWInfo->eDistinct ){
      VdbeOp *pOp;                /* No longer required OpenEphemeral instr. */
     
      assert( addrDistinctIndex>=0 );
      sqlite3VdbeChangeToNoop(v, addrDistinctIndex);
      pOp = sqlite3VdbeGetOp(v, addrDistinctIndex);

      assert( isDistinct );
      assert( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED 
           || pWInfo->eDistinct==WHERE_DISTINCT_UNIQUE 
      );
      distinctTab = -1;
      if( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED ){
        int iJump;
        int iExpr;
        int nExpr = pEList->nExpr;
        int iBase = pParse->nMem+1;
        int iBase2 = iBase + nExpr;
        pParse->nMem += (pEList->nExpr*2);

        /* Change the OP_OpenEphemeral coded earlier to an OP_Null
        ** sets the MEM_Cleared bit on the first register of the
        ** previous value.  This will cause the OP_Ne below to always
        ** fail on the first iteration of the loop even if the first
        ** row is all NULLs.
        */
        pOp->opcode = OP_Null;
        pOp->p1 = 1;
        pOp->p2 = iBase2;


        sqlite3ExprCodeExprList(pParse, pEList, iBase, 1);
        iJump = sqlite3VdbeCurrentAddr(v) + pEList->nExpr;
        for(iExpr=0; iExpr<nExpr; iExpr++){
          CollSeq *pColl = sqlite3ExprCollSeq(pParse, pEList->a[iExpr].pExpr);
          if( iExpr<nExpr-1 ){
            sqlite3VdbeAddOp3(v, OP_Ne, iBase+iExpr, iJump, iBase2+iExpr);
          }else{
            sqlite3VdbeAddOp3(v, OP_Eq, iBase+iExpr, pWInfo->iContinue,
                              iBase2+iExpr);
          }
          sqlite3VdbeChangeP4(v, -1, (const char *)pColl, P4_COLLSEQ);
          sqlite3VdbeChangeP5(v, SQLITE_NULLEQ);
        }
        assert( sqlite3VdbeCurrentAddr(v)==iJump );
        sqlite3VdbeAddOp3(v, OP_Move, iBase, iBase2, pEList->nExpr);


      }
    }

    /* Use the standard inner loop. */
    selectInnerLoop(pParse, p, pEList, 0, 0, pOrderBy, distinctTab, pDest,
                    pWInfo->iContinue, pWInfo->iBreak);

    /* End the database scan loop.
    */
    sqlite3WhereEnd(pWInfo);
  }else{
    /* This is the processing for aggregate queries */

      addrOutputRow = sqlite3VdbeCurrentAddr(v);
      sqlite3VdbeAddOp2(v, OP_IfPos, iUseFlag, addrOutputRow+2);
      VdbeComment((v, "Groupby result generator entry point"));
      sqlite3VdbeAddOp1(v, OP_Return, regOutputRow);
      finalizeAggFunctions(pParse, &sAggInfo);
      sqlite3ExprIfFalse(pParse, pHaving, addrOutputRow+1, SQLITE_JUMPIFNULL);
      selectInnerLoop(pParse, p, p->pEList, 0, 0, pOrderBy,
                      distinctTab, pDest,
                      addrOutputRow+1, addrSetAbort);
      sqlite3VdbeAddOp1(v, OP_Return, regOutputRow);
      VdbeComment((v, "end groupby result generator"));

      /* Generate a subroutine that will reset the group-by accumulator
      */
      sqlite3VdbeResolveLabel(v, addrReset);

                      pDest, addrEnd, addrEnd);
      sqlite3ExprListDelete(db, pDel);
    }
    sqlite3VdbeResolveLabel(v, addrEnd);
    
  } /* endif aggregate query */

  if( distinctTab>=0 ){
    explainTempTable(pParse, "DISTINCT");
  }

  /* 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 ){

** addrOpenEphm[] entries contain the address of OP_OpenEphemeral opcodes.
** These addresses must be stored so that we can go back and fill in
** the P4_KEYINFO and P2 parameters later.  Neither the KeyInfo nor
** the number of columns in P2 can be computed at the same time
** as the OP_OpenEphm instruction is coded because not
** enough information about the compound query is known at that point.
** The KeyInfo for addrOpenTran[0] and [1] contains collating sequences
** for the result set.  The KeyInfo for addrOpenEphm[2] contains collating
** sequences for the ORDER BY clause.
*/
struct Select {
  ExprList *pEList;      /* The fields of the result */
  u8 op;                 /* One of: TK_UNION TK_ALL TK_INTERSECT TK_EXCEPT */
  char affinity;         /* MakeRecord with this affinity for SRT_Set */
  u16 selFlags;          /* Various SF_* values */