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Overview
Comment:Bring some comments up to date in the query planner, and especially the ORDER BY optimizer. Also add testcase() macros.
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SHA1: bb5c0f1c92b48631d4a12cd4f321b53cd07885c8
User & Date: drh 2012-10-09 09:26:28
Context
2012-10-09
14:36
Avoid an assertion fault and/or freeing memory while it is still in use when an error occurs during virtual table construction. check-in: a02599ad user: drh tags: trunk
09:26
Bring some comments up to date in the query planner, and especially the ORDER BY optimizer. Also add testcase() macros. check-in: bb5c0f1c user: drh tags: trunk
01:39
Remove an unused variable. Fix code that occurs before a variable declaration. check-in: 01dc032b user: drh tags: trunk
Changes
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Changes to src/where.c.

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** clause, either in whole or in part.  The return value is the 
** cumulative number of terms in the ORDER BY clause that are satisfied
** by the index pIdx and other indices in outer loops.
**
** The table being queried has a cursor number of "base".  pIdx is the
** index that is postulated for use to access the table.
**
** nEqCol is the number of columns of pIdx that are used as equality
** constraints and where the other side of the == is an ordered column
** or constant.  An "order column" in the previous sentence means a column
** in table from an outer loop whose values will always appear in the 
** correct order due to othre index, or because the outer loop generates
** a unique result.  Any of the first nEqCol columns of pIdx may be missing
** from the ORDER BY clause and the match can still be a success.
**
** The *pbRev value is set to 0 order 1 depending on whether or not
** pIdx should be run in the forward order or in reverse order.
*/
static int isSortingIndex(
  WhereBestIdx *p,    /* Best index search context */
  Index *pIdx,        /* The index we are testing */
  int base,           /* Cursor number for the table to be sorted */
................................................................................
    }else{
      isMatch = 0;
    }

    /* termSortOrder is 0 or 1 for whether or not the access loop should
    ** run forward or backwards (respectively) in order to satisfy this 
    ** term of the ORDER BY clause. */


    termSortOrder = iSortOrder ^ pOBItem->sortOrder;

    /* If X is the column in the index and ORDER BY clause, check to see
    ** if there are any X= or X IS NULL constraints in the WHERE clause. */
    pConstraint = findTerm(p->pWC, base, iColumn, p->notReady,
                           WO_EQ|WO_ISNULL|WO_IN, pIdx);
    if( pConstraint==0 ){
      isEq = 0;
    }else if( pConstraint->eOperator==WO_IN ){



      break;
    }else if( pConstraint->eOperator==WO_ISNULL ){
      uniqueNotNull = 0;
      isEq = 1;
    }else if( pConstraint->prereqRight==0 ){
      isEq = 1;
    }else{
      Expr *pRight = pConstraint->pExpr->pRight;
      if( pRight->op==TK_COLUMN ){
        WHERETRACE(("       .. isOrderedColumn(tab=%d,col=%d)",
                    pRight->iTable, pRight->iColumn));
        isEq = isOrderedColumn(p, pRight->iTable, pRight->iColumn);
        WHERETRACE((" -> isEq=%d\n", isEq));




        if( isMatch && isEq>=2 && isEq!=pOBItem->sortOrder+2 ){


          break;
        }
      }else{
        isEq = 0;
      }
    }
    assert( pOBItem->sortOrder==0 || pOBItem->sortOrder==1 );
    assert( iSortOrder==0 || iSortOrder==1 );
    if( !isMatch ){
      if( isEq==0 ){
        break;
      }else{
        continue;
      }
    }else if( isEq!=1 ){
................................................................................
      }
    }
    j++;
    pOBItem++;
    if( iColumn<0 ){
      seenRowid = 1;
      break;
    }else if( pTab->aCol[iColumn].notNull==0 && isEq==0 ){



      uniqueNotNull = 0;
    }
  }

  /* If we have not found at least one ORDER BY term that matches the
  ** index, then show no progress. */
  if( pOBItem==&pOrderBy->a[nPriorSat] ) return nPriorSat;







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** clause, either in whole or in part.  The return value is the 
** cumulative number of terms in the ORDER BY clause that are satisfied
** by the index pIdx and other indices in outer loops.
**
** The table being queried has a cursor number of "base".  pIdx is the
** index that is postulated for use to access the table.
**








** The *pbRev value is set to 0 order 1 depending on whether or not
** pIdx should be run in the forward order or in reverse order.
*/
static int isSortingIndex(
  WhereBestIdx *p,    /* Best index search context */
  Index *pIdx,        /* The index we are testing */
  int base,           /* Cursor number for the table to be sorted */
................................................................................
    }else{
      isMatch = 0;
    }

    /* termSortOrder is 0 or 1 for whether or not the access loop should
    ** run forward or backwards (respectively) in order to satisfy this 
    ** term of the ORDER BY clause. */
    assert( pOBItem->sortOrder==0 || pOBItem->sortOrder==1 );
    assert( iSortOrder==0 || iSortOrder==1 );
    termSortOrder = iSortOrder ^ pOBItem->sortOrder;

    /* If X is the column in the index and ORDER BY clause, check to see
    ** if there are any X= or X IS NULL constraints in the WHERE clause. */
    pConstraint = findTerm(p->pWC, base, iColumn, p->notReady,
                           WO_EQ|WO_ISNULL|WO_IN, pIdx);
    if( pConstraint==0 ){
      isEq = 0;
    }else if( pConstraint->eOperator==WO_IN ){
      /* Constraints of the form: "X IN ..." cannot be used with an ORDER BY
      ** because we do not know in what order the values on the RHS of the IN
      ** operator will occur. */
      break;
    }else if( pConstraint->eOperator==WO_ISNULL ){
      uniqueNotNull = 0;
      isEq = 1;  /* "X IS NULL" means X has only a single value */
    }else if( pConstraint->prereqRight==0 ){
      isEq = 1;  /* Constraint "X=constant" means X has only a single value */
    }else{
      Expr *pRight = pConstraint->pExpr->pRight;
      if( pRight->op==TK_COLUMN ){
        WHERETRACE(("       .. isOrderedColumn(tab=%d,col=%d)",
                    pRight->iTable, pRight->iColumn));
        isEq = isOrderedColumn(p, pRight->iTable, pRight->iColumn);
        WHERETRACE((" -> isEq=%d\n", isEq));

        /* If the constraint is of the form X=Y where Y is an ordered value
        ** in an outer loop, then make sure the sort order of Y matches the
        ** sort order required for X. */
        if( isMatch && isEq>=2 && isEq!=pOBItem->sortOrder+2 ){
          testcase( isEq==2 );
          testcase( isEq==3 );
          break;
        }
      }else{
        isEq = 0;  /* "X=expr" places no ordering constraints on X */
      }
    }


    if( !isMatch ){
      if( isEq==0 ){
        break;
      }else{
        continue;
      }
    }else if( isEq!=1 ){
................................................................................
      }
    }
    j++;
    pOBItem++;
    if( iColumn<0 ){
      seenRowid = 1;
      break;
    }else if( pTab->aCol[iColumn].notNull==0 && isEq!=1 ){
      testcase( isEq==0 );
      testcase( isEq==2 );
      testcase( isEq==3 );
      uniqueNotNull = 0;
    }
  }

  /* If we have not found at least one ORDER BY term that matches the
  ** index, then show no progress. */
  if( pOBItem==&pOrderBy->a[nPriorSat] ) return nPriorSat;