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Overview
Comment:Fix the skip-ahead-distinct optimization so that it works with indexes that have repeated columns with different collating sequences.
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SHA3-256:ce1e2b88777e00a82c04abe5ba35eec81b5f324e462f099cd00b21054f369688
User & Date: drh 2017-04-13 21:29:02
Context
2017-04-14
00:45
Fix a couple of unreachable branches. check-in: 1aa0ea8d user: drh tags: skip-ahead-distinct
2017-04-13
21:29
Fix the skip-ahead-distinct optimization so that it works with indexes that have repeated columns with different collating sequences. check-in: ce1e2b88 user: drh tags: skip-ahead-distinct
19:48
Simplification of the skip-ahead-distinct logic. There is still an issue with handling COLLATE. check-in: 57c5173b user: drh tags: skip-ahead-distinct
Changes
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Changes to src/where.c.

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      if( wctrlFlags & WHERE_ORDERBY_LIMIT ) continue;
    }else{
      pLoop = pLast;
    }
    if( pLoop->wsFlags & WHERE_VIRTUALTABLE ){
      if( pLoop->u.vtab.isOrdered ) obSat = obDone;
      break;


    }
    iCur = pWInfo->pTabList->a[pLoop->iTab].iCursor;

    /* Mark off any ORDER BY term X that is a column in the table of
    ** the current loop for which there is term in the WHERE
    ** clause of the form X IS NULL or X=? that reference only outer
    ** loops.
................................................................................
            }
          }
          if( iColumn>=0 ){
            pColl = sqlite3ExprCollSeq(pWInfo->pParse, pOrderBy->a[i].pExpr);
            if( !pColl ) pColl = db->pDfltColl;
            if( sqlite3StrICmp(pColl->zName, pIndex->azColl[j])!=0 ) continue;
          }

          isMatch = 1;
          break;
        }
        if( isMatch && (wctrlFlags & WHERE_GROUPBY)==0 ){
          /* Make sure the sort order is compatible in an ORDER BY clause.
          ** Sort order is irrelevant for a GROUP BY clause. */
          if( revSet ){
................................................................................
  for(i=pWInfo->nLevel-1; i>=0; i--){
    int addr;
    pLevel = &pWInfo->a[i];
    pLoop = pLevel->pWLoop;
    if( pLevel->op!=OP_Noop ){
#ifndef SQLITE_DISABLE_SKIPAHEAD_DISTINCT
      int addrSeek = 0;
      int n = -1;
      int j, k, op;
      int r1 = pParse->nMem+1;
      Index *pIdx;

      if( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED
       && (pLoop->wsFlags & WHERE_INDEXED)!=0
       && OptimizationEnabled(db, SQLITE_SkipAhead)
       && (pIdx = pLoop->u.btree.pIndex)->hasStat1

      ){
        /* 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. */
        ExprList *pX = pWInfo->pResultSet;
        for(j=0; j<pX->nExpr; j++){
          Expr *pE = sqlite3ExprSkipCollate(pX->a[j].pExpr);
          if( pE->op==TK_COLUMN ){
            if( pE->iTable==pLevel->iIdxCur ){
              k = pE->iColumn+1;
            }else{
              if( pE->iTable!=pLevel->iTabCur ) continue;
              k = 1+sqlite3ColumnOfIndex(pIdx, pE->iColumn);
            }
            if( k>n ) n = k;
          }
#ifdef SQLITE_DEBUG
          /* Any expressions in the result-set that match columns of the
          ** index should have already been transformed to TK_COLUMN 
          ** operations by whereIndexExprTrans().  */
          else if( pIdx->aColExpr ){
            for(k=0; k<pIdx->nKeyCol; k++){
              Expr *pI = pIdx->aColExpr->a[k].pExpr;
              assert( pI==0 || sqlite3ExprCompare(pE, pI, pE->iTable)!=0 );
            }
          }
#endif
        }
      }
      /* TUNING: Only try to skip ahead using OP_Seek if we expect to
      ** skip over 11 or more rows.  Otherwise, OP_Next is just as fast.
      */
      assert( 36==sqlite3LogEst(12) );
      if( n>0 && pIdx->aiRowLogEst[n]>=36 ){
        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;
        addrSeek = 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);
      }
#endif /* SQLITE_DISABLE_SKIPAHEAD_DISTINCT */







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      if( wctrlFlags & WHERE_ORDERBY_LIMIT ) continue;
    }else{
      pLoop = pLast;
    }
    if( pLoop->wsFlags & WHERE_VIRTUALTABLE ){
      if( pLoop->u.vtab.isOrdered ) obSat = obDone;
      break;
    }else{
      pLoop->u.btree.nIdxCol = 0;
    }
    iCur = pWInfo->pTabList->a[pLoop->iTab].iCursor;

    /* Mark off any ORDER BY term X that is a column in the table of
    ** the current loop for which there is term in the WHERE
    ** clause of the form X IS NULL or X=? that reference only outer
    ** loops.
................................................................................
            }
          }
          if( iColumn>=0 ){
            pColl = sqlite3ExprCollSeq(pWInfo->pParse, pOrderBy->a[i].pExpr);
            if( !pColl ) pColl = db->pDfltColl;
            if( sqlite3StrICmp(pColl->zName, pIndex->azColl[j])!=0 ) continue;
          }
          if( pLoop->u.btree.nIdxCol<=j ) pLoop->u.btree.nIdxCol = j+1;
          isMatch = 1;
          break;
        }
        if( isMatch && (wctrlFlags & WHERE_GROUPBY)==0 ){
          /* Make sure the sort order is compatible in an ORDER BY clause.
          ** Sort order is irrelevant for a GROUP BY clause. */
          if( revSet ){
................................................................................
  for(i=pWInfo->nLevel-1; i>=0; i--){
    int addr;
    pLevel = &pWInfo->a[i];
    pLoop = pLevel->pWLoop;
    if( pLevel->op!=OP_Noop ){
#ifndef SQLITE_DISABLE_SKIPAHEAD_DISTINCT
      int addrSeek = 0;



      Index *pIdx;
      int n;
      if( pWInfo->eDistinct==WHERE_DISTINCT_ORDERED
       && (pLoop->wsFlags & WHERE_INDEXED)!=0
       && OptimizationEnabled(db, SQLITE_SkipAhead)
       && (pIdx = pLoop->u.btree.pIndex)->hasStat1
       && pIdx->aiRowLogEst[(n = pLoop->u.btree.nIdxCol)-1]>=36
      ){

        int r1 = pParse->nMem+1;
        int j, op;































        for(j=0; j<n; j++){
          sqlite3VdbeAddOp3(v, OP_Column, pLevel->iIdxCur, j, r1+j);
        }
        pParse->nMem += n+1;
        op = pLevel->op==OP_Prev ? OP_SeekLT : OP_SeekGT;
        addrSeek = 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);
      }
#endif /* SQLITE_DISABLE_SKIPAHEAD_DISTINCT */

Changes to src/whereInt.h.

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  LogEst rRun;          /* Cost of running each loop */
  LogEst nOut;          /* Estimated number of output rows */
  union {
    struct {               /* Information for internal btree tables */
      u16 nEq;               /* Number of equality constraints */
      u16 nBtm;              /* Size of BTM vector */
      u16 nTop;              /* Size of TOP vector */

      Index *pIndex;         /* Index used, or NULL */
    } btree;
    struct {               /* Information for virtual tables */
      int idxNum;            /* Index number */
      u8 needFree;           /* True if sqlite3_free(idxStr) is needed */
      i8 isOrdered;          /* True if satisfies ORDER BY */
      u16 omitMask;          /* Terms that may be omitted */







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  LogEst rRun;          /* Cost of running each loop */
  LogEst nOut;          /* Estimated number of output rows */
  union {
    struct {               /* Information for internal btree tables */
      u16 nEq;               /* Number of equality constraints */
      u16 nBtm;              /* Size of BTM vector */
      u16 nTop;              /* Size of TOP vector */
      u16 nIdxCol;           /* Index column used for ORDER BY */
      Index *pIndex;         /* Index used, or NULL */
    } btree;
    struct {               /* Information for virtual tables */
      int idxNum;            /* Index number */
      u8 needFree;           /* True if sqlite3_free(idxStr) is needed */
      i8 isOrdered;          /* True if satisfies ORDER BY */
      u16 omitMask;          /* Terms that may be omitted */

Changes to test/distinct2.test.

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do_execsql_test 830 {
  CREATE INDEX i8 ON t8(a, c);
  ANALYZE;
  SELECT DISTINCT a, b, c FROM t8 WHERE b=3;
} {1 3 1}











finish_test







































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do_execsql_test 830 {
  CREATE INDEX i8 ON t8(a, c);
  ANALYZE;
  SELECT DISTINCT a, b, c FROM t8 WHERE b=3;
} {1 3 1}

do_execsql_test 900 {
  CREATE TABLE t9(v);
  INSERT INTO t9 VALUES 
    ('abcd'), ('Abcd'), ('aBcd'), ('ABcd'), ('abCd'), ('AbCd'), ('aBCd'), 
    ('ABCd'), ('abcD'), ('AbcD'), ('aBcD'), ('ABcD'), ('abCD'), ('AbCD'), 
    ('aBCD'), ('ABCD'),
    ('wxyz'), ('Wxyz'), ('wXyz'), ('WXyz'), ('wxYz'), ('WxYz'), ('wXYz'), 
    ('WXYz'), ('wxyZ'), ('WxyZ'), ('wXyZ'), ('WXyZ'), ('wxYZ'), ('WxYZ'), 
    ('wXYZ'), ('WXYZ');
}


do_execsql_test 910 {
  SELECT DISTINCT v COLLATE NOCASE, v FROM t9 ORDER BY +v;
} {
  ABCD ABCD ABCd ABCd ABcD ABcD ABcd ABcd AbCD
  AbCD AbCd AbCd AbcD AbcD Abcd Abcd
  WXYZ WXYZ WXYz WXYz WXyZ WXyZ WXyz WXyz WxYZ
  WxYZ WxYz WxYz WxyZ WxyZ Wxyz Wxyz
  aBCD aBCD aBCd aBCd aBcD aBcD aBcd aBcd abCD
  abCD abCd abCd abcD abcD abcd abcd
  wXYZ wXYZ wXYz wXYz wXyZ wXyZ wXyz wXyz wxYZ
  wxYZ wxYz wxYz wxyZ wxyZ wxyz wxyz
}

do_execsql_test 920 {
  CREATE INDEX i9 ON t9(v COLLATE NOCASE, v);
  ANALYZE;

  SELECT DISTINCT v COLLATE NOCASE, v FROM t9 ORDER BY +v;
} {
  ABCD ABCD ABCd ABCd ABcD ABcD ABcd ABcd AbCD
  AbCD AbCd AbCd AbcD AbcD Abcd Abcd
  WXYZ WXYZ WXYz WXYz WXyZ WXyZ WXyz WXyz WxYZ
  WxYZ WxYz WxYz WxyZ WxyZ Wxyz Wxyz
  aBCD aBCD aBCd aBCd aBcD aBcD aBcd aBcd abCD
  abCD abCd abCd abcD abcD abcd abcd
  wXYZ wXYZ wXYz wXYz wXyZ wXyZ wXyz wXyz wxYZ
  wxYZ wxYz wxYz wxyZ wxyZ wxyz wxyz
}


finish_test