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Overview
Comment:Remove a pointless OP_Once operation in ORDER BY clauses with LIMIT.
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Timelines: family | ancestors | descendants | both | orderby-planning
Files: files | file ages | folders
SHA1: e6c59d23316c83b318b1a94d9b28a5d321737fa5
User & Date: drh 2014-03-24 02:20:53.278
Context
2014-03-24
09:34
Remove an unnecessary temporary register allocation. (check-in: 5d506743f5 user: dan tags: orderby-planning)
02:20
Remove a pointless OP_Once operation in ORDER BY clauses with LIMIT. (check-in: e6c59d2331 user: drh tags: orderby-planning)
01:43
Further enhancements to generated VDBE code for ORDER BY. (check-in: e7188fad87 user: drh tags: orderby-planning)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/select.c.
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  struct ExprList_item *aOutEx = p->pEList->a;
#endif

  if( pSort->labelBkOut ){
    sqlite3VdbeAddOp2(v, OP_Gosub, pSort->regReturn, pSort->labelBkOut);
    sqlite3VdbeAddOp2(v, OP_Goto, 0, addrBreak);
    sqlite3VdbeResolveLabel(v, pSort->labelBkOut);
    addrOnce = sqlite3CodeOnce(pParse); VdbeCoverage(v);
  }
  iTab = pSort->iECursor;
  regRow = sqlite3GetTempReg(pParse);
  if( eDest==SRT_Output || eDest==SRT_Coroutine ){
    regRowid = 0;
    regRow = pDest->iSdst;
    nSortData = nColumn;
  }else{
    regRowid = sqlite3GetTempReg(pParse);
    regRow = sqlite3GetTempReg(pParse);
    nSortData = 1;
  }
  nKey = pOrderBy->nExpr - pSort->nOBSat;
  if( pSort->sortFlags & SORTFLAG_UseSorter ){
    int regSortOut = ++pParse->nMem;
    iSortTab = pParse->nTab++;



    sqlite3VdbeAddOp3(v, OP_OpenPseudo, iSortTab, regSortOut, nKey+1+nSortData);
    if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
    addr = 1 + sqlite3VdbeAddOp2(v, OP_SorterSort, iTab, addrBreak);
    VdbeCoverage(v);
    codeOffset(v, p->iOffset, addrContinue);
    sqlite3VdbeAddOp2(v, OP_SorterData, iTab, regSortOut);
    p5 = OPFLAG_CLEARCACHE;
  }else{
    if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
    addr = 1 + sqlite3VdbeAddOp2(v, OP_Sort, iTab, addrBreak); VdbeCoverage(v);
    codeOffset(v, p->iOffset, addrContinue);
    sqlite3VdbeAddOp3(v, OP_Column, iTab, nKey+1, regRow);
    iSortTab = iTab;
    p5 = 0;
  }
  for(i=0; i<nSortData; i++){
    sqlite3VdbeAddOp3(v, OP_Column, iSortTab, nKey+1+i, regRow+i);
    if( i==0 ) sqlite3VdbeChangeP5(v, p5);
    VdbeComment((v, "%s", aOutEx[i].zName ? aOutEx[i].zName : aOutEx[i].zSpan));








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  struct ExprList_item *aOutEx = p->pEList->a;
#endif

  if( pSort->labelBkOut ){
    sqlite3VdbeAddOp2(v, OP_Gosub, pSort->regReturn, pSort->labelBkOut);
    sqlite3VdbeAddOp2(v, OP_Goto, 0, addrBreak);
    sqlite3VdbeResolveLabel(v, pSort->labelBkOut);

  }
  iTab = pSort->iECursor;
  regRow = sqlite3GetTempReg(pParse);
  if( eDest==SRT_Output || eDest==SRT_Coroutine ){
    regRowid = 0;
    regRow = pDest->iSdst;
    nSortData = nColumn;
  }else{
    regRowid = sqlite3GetTempReg(pParse);
    regRow = sqlite3GetTempReg(pParse);
    nSortData = 1;
  }
  nKey = pOrderBy->nExpr - pSort->nOBSat;
  if( pSort->sortFlags & SORTFLAG_UseSorter ){
    int regSortOut = ++pParse->nMem;
    iSortTab = pParse->nTab++;
    if( pSort->labelBkOut ){
      addrOnce = sqlite3CodeOnce(pParse); VdbeCoverage(v);
    }
    sqlite3VdbeAddOp3(v, OP_OpenPseudo, iSortTab, regSortOut, nKey+1+nSortData);
    if( addrOnce ) sqlite3VdbeJumpHere(v, addrOnce);
    addr = 1 + sqlite3VdbeAddOp2(v, OP_SorterSort, iTab, addrBreak);
    VdbeCoverage(v);
    codeOffset(v, p->iOffset, addrContinue);
    sqlite3VdbeAddOp2(v, OP_SorterData, iTab, regSortOut);
    p5 = OPFLAG_CLEARCACHE;
  }else{

    addr = 1 + sqlite3VdbeAddOp2(v, OP_Sort, iTab, addrBreak); VdbeCoverage(v);
    codeOffset(v, p->iOffset, addrContinue);

    iSortTab = iTab;
    p5 = 0;
  }
  for(i=0; i<nSortData; i++){
    sqlite3VdbeAddOp3(v, OP_Column, iSortTab, nKey+1+i, regRow+i);
    if( i==0 ) sqlite3VdbeChangeP5(v, p5);
    VdbeComment((v, "%s", aOutEx[i].zName ? aOutEx[i].zName : aOutEx[i].zSpan));
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