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Overview
Comment:Fixes to the skip-ahead distinct logic. More issues remain.
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Timelines: family | ancestors | descendants | both | skip-ahead-distinct
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SHA1: 45a70b2bb8f7b465bab45d2eaad24d372b1afe61
User & Date: drh 2016-04-15 15:54:17.966
Context
2016-04-15
16:17
Skip-ahead does not always work. So we still have to check for redundancy. (check-in: db5a2364eb user: drh tags: skip-ahead-distinct)
15:54
Fixes to the skip-ahead distinct logic. More issues remain. (check-in: 45a70b2bb8 user: drh tags: skip-ahead-distinct)
15:06
Merge enhancements from trunk, especially the ".eqp full" enhancement to the command-line shell. (check-in: 491f0dbd63 user: drh tags: skip-ahead-distinct)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/where.c.
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    pLevel = &pWInfo->a[i];
    pLoop = pLevel->pWLoop;
    sqlite3VdbeResolveLabel(v, pLevel->addrCont);
    if( pLevel->op!=OP_Noop ){
      if( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED
       && (pLoop->wsFlags & WHERE_INDEXED)!=0
      ){




        int j, k, op;
        int r1 = pParse->nMem+1;
        int n = 0;
        ExprList *pX = pWInfo->pDistinctSet;

        for(j=0; j<pX->nExpr; j++){
          Expr *pE = sqlite3ExprSkipCollate(pX->a[j].pExpr);
          if( pE->op==TK_COLUMN && pE->iTable==pLevel->iTabCur ) n++;









        }




        for(j=0; j<n; j++){
          sqlite3VdbeAddOp3(v, OP_Column, pLevel->iIdxCur, j, r1+j);
        }
        pParse->nMem += n;
        if( n>0 ){
          op = pLevel->op==OP_Prev ? OP_SeekLT : OP_SeekGT;
          k = sqlite3VdbeAddOp4Int(v, op, pLevel->iIdxCur, 0, r1, n);
          VdbeCoverageIf(v, op==OP_SeekLT);
          VdbeCoverageIf(v, op==OP_SeekGT);
          sqlite3VdbeAddOp2(v, OP_Goto, 1, pLevel->p2);
          sqlite3VdbeJumpHere(v, k);
        }
      }else{

        sqlite3VdbeAddOp3(v, pLevel->op, pLevel->p1, pLevel->p2, pLevel->p3);
        sqlite3VdbeChangeP5(v, pLevel->p5);
        VdbeCoverage(v);
        VdbeCoverageIf(v, pLevel->op==OP_Next);
        VdbeCoverageIf(v, pLevel->op==OP_Prev);
        VdbeCoverageIf(v, pLevel->op==OP_VNext);
      }








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    pLevel = &pWInfo->a[i];
    pLoop = pLevel->pWLoop;
    sqlite3VdbeResolveLabel(v, pLevel->addrCont);
    if( pLevel->op!=OP_Noop ){
      if( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED
       && (pLoop->wsFlags & WHERE_INDEXED)!=0
      ){
        /* This is the Skip-ahead optimization.  When doing a DISTINCT query
        ** that has WHERE_DISTINCT_ORDERED, use OP_SkipGT/OP_SkipLT to skip
        ** over all duplicate entries, rather than visiting all duplicates
        ** using OP_Next/OP_Prev. */
        int j, k, op;
        int r1 = pParse->nMem+1;
        int n = -1;
        ExprList *pX = pWInfo->pDistinctSet;
        Index *pIdx = pLoop->u.btree.pIndex;
        for(j=0; j<pX->nExpr; j++){
          Expr *pE = sqlite3ExprSkipCollate(pX->a[j].pExpr);
          if( pE->op==TK_COLUMN ){
            if( pE->iTable!=pLevel->iTabCur ) continue;
            k = 1+sqlite3ColumnOfIndex(pIdx, pE->iColumn);
            if( k>n ) n = k;
          }else if( pIdx->aColExpr ){
            for(k=n+1; k<pIdx->nKeyCol; k++){
              Expr *pI = pIdx->aColExpr->a[k].pExpr;
              if( pI && sqlite3ExprCompare(pE,pI,0)<2 ){
                n = k+1;
                break;
              }
            }
          }
        }
        if( n>0 ){
          for(j=0; j<n; j++){
            sqlite3VdbeAddOp3(v, OP_Column, pLevel->iIdxCur, j, r1+j);
          }
          pParse->nMem += n;

          op = pLevel->op==OP_Prev ? OP_SeekLT : OP_SeekGT;
          k = sqlite3VdbeAddOp4Int(v, op, pLevel->iIdxCur, 0, r1, n);
          VdbeCoverageIf(v, op==OP_SeekLT);
          VdbeCoverageIf(v, op==OP_SeekGT);
          sqlite3VdbeAddOp2(v, OP_Goto, 1, pLevel->p2);
          sqlite3VdbeJumpHere(v, k);
        }
      }else{
        /* The common case: Advance to the next row */
        sqlite3VdbeAddOp3(v, pLevel->op, pLevel->p1, pLevel->p2, pLevel->p3);
        sqlite3VdbeChangeP5(v, pLevel->p5);
        VdbeCoverage(v);
        VdbeCoverageIf(v, pLevel->op==OP_Next);
        VdbeCoverageIf(v, pLevel->op==OP_Prev);
        VdbeCoverageIf(v, pLevel->op==OP_VNext);
      }
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