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SQLite training in Houston TX on 2019-11-05 (details)
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Overview
Comment:Cherrypicked from trunk: Do not try to use STAT2 for row estimates if the index is unique or nearly so.
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SHA1: d55b64ef7e04e10a31360dea55751a33a0d591a4
User & Date: drh 2011-07-13 18:53:13
Context
2011-08-26
17:17
Cherrypick the recursion fix to test_vfs.c from [065e5a5ea4f82]. Also fix the nan.test module to handle upper/lower case changes in TCL. check-in: 41b5f869 user: drh tags: branch-3.7.2
13:52
Merge branches branch-3.7.2 and stat3-enhancement into a new branch for testing purposes. check-in: 0df04f92 user: drh tags: stat3-3.7.2
2011-07-13
18:53
Cherrypicked from trunk: Do not try to use STAT2 for row estimates if the index is unique or nearly so. check-in: d55b64ef user: drh tags: branch-3.7.2
2011-07-12
14:48
Cherrypick change [9f14fa56ba] (the fix for [54844eea3f]) from the trunk. check-in: 7afb2354 user: dan tags: branch-3.7.2
Changes
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Changes to src/where.c.

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    nRow = (double)(aiRowEst[nEq] * nInMul);
    if( bInEst && nRow*2>aiRowEst[0] ){
      nRow = aiRowEst[0]/2;
      nInMul = (int)(nRow / aiRowEst[nEq]);
    }

#ifdef SQLITE_ENABLE_STAT2
    /* If the constraint is of the form x=VALUE and histogram

    ** data is available for column x, then it might be possible
    ** to get a better estimate on the number of rows based on
    ** VALUE and how common that value is according to the histogram.
    */
    if( nRow>(double)1 && nEq==1 && pFirstTerm!=0 ){
      if( pFirstTerm->eOperator & (WO_EQ|WO_ISNULL) ){
        testcase( pFirstTerm->eOperator==WO_EQ );
        testcase( pFirstTerm->pOperator==WO_ISNULL );
        whereEqualScanEst(pParse, pProbe, pFirstTerm->pExpr->pRight, &nRow);
      }else if( pFirstTerm->eOperator==WO_IN && bInEst==0 ){
        whereInScanEst(pParse, pProbe, pFirstTerm->pExpr->x.pList, &nRow);
      }







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    nRow = (double)(aiRowEst[nEq] * nInMul);
    if( bInEst && nRow*2>aiRowEst[0] ){
      nRow = aiRowEst[0]/2;
      nInMul = (int)(nRow / aiRowEst[nEq]);
    }

#ifdef SQLITE_ENABLE_STAT2
    /* If the constraint is of the form x=VALUE or x IN (E1,E2,...)
    ** and we do not think that values of x are unique and if histogram
    ** data is available for column x, then it might be possible
    ** to get a better estimate on the number of rows based on
    ** VALUE and how common that value is according to the histogram.
    */
    if( nRow>(double)1 && nEq==1 && pFirstTerm!=0 && aiRowEst[1]>1 ){
      if( pFirstTerm->eOperator & (WO_EQ|WO_ISNULL) ){
        testcase( pFirstTerm->eOperator==WO_EQ );
        testcase( pFirstTerm->pOperator==WO_ISNULL );
        whereEqualScanEst(pParse, pProbe, pFirstTerm->pExpr->pRight, &nRow);
      }else if( pFirstTerm->eOperator==WO_IN && bInEst==0 ){
        whereInScanEst(pParse, pProbe, pFirstTerm->pExpr->x.pList, &nRow);
      }