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Overview
Comment:Allow an index paired with an IS NULL constraint to be used for sorting under the condition that the index be treated as a non-unique index.
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SHA1: d78949fc93077e1aa7f05cf9f7e947727939cc96
User & Date: drh 2011-02-11 03:56:11
Original Comment: Allow an index paired with a NOT NULL constraint to be used for sorting under the condition that the index be treated as a non-unique index.
Context
2011-02-11
06:59
Fix a bug in the new WHERE-clause processing that tries to use an index to resolve IS NOT NULL constraints when SQLITE_ENABLE_STAT2 is defined. The bug could cause memory overruns and segfaults. The bug was new to the code and has not appeared in an official release. Found during structural testing. check-in: a5c36b9f user: drh tags: trunk
03:56
Allow an index paired with an IS NULL constraint to be used for sorting under the condition that the index be treated as a non-unique index. check-in: d78949fc user: drh tags: trunk
02:43
Disable unused NULL tests when SQLITE_ENABLE_STAT2 is not in use. check-in: 5ecd1178 user: drh tags: trunk
Changes
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Changes to src/where.c.

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static int isSortingIndex(
  Parse *pParse,          /* Parsing context */
  WhereMaskSet *pMaskSet, /* Mapping from table cursor numbers to bitmaps */
  Index *pIdx,            /* The index we are testing */
  int base,               /* Cursor number for the table to be sorted */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  int nEqCol,             /* Number of index columns with == constraints */

  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  int i, j;                       /* Loop counters */
  int sortOrder = 0;              /* XOR of index and ORDER BY sort direction */
  int nTerm;                      /* Number of ORDER BY terms */
  struct ExprList_item *pTerm;    /* A term of the ORDER BY clause */
  sqlite3 *db = pParse->db;
................................................................................
  *pbRev = sortOrder!=0;
  if( j>=nTerm ){
    /* All terms of the ORDER BY clause are covered by this index so
    ** this index can be used for sorting. */
    return 1;
  }
  if( pIdx->onError!=OE_None && i==pIdx->nColumn

      && !referencesOtherTables(pOrderBy, pMaskSet, j, base) ){
    /* All terms of this index match some prefix of the ORDER BY clause
    ** and the index is UNIQUE and no terms on the tail of the ORDER BY
    ** clause reference other tables in a join.  If this is all true then
    ** the order by clause is superfluous. */


    return 1;
  }
  return 0;
}

/*
** Prepare a crude estimate of the logarithm of the input value.
................................................................................
    }

    /* If there is an ORDER BY clause and the index being considered will
    ** naturally scan rows in the required order, set the appropriate flags
    ** in wsFlags. Otherwise, if there is an ORDER BY clause but the index
    ** will scan rows in a different order, set the bSort variable.  */
    if( pOrderBy ){
      if( (wsFlags & (WHERE_COLUMN_IN|WHERE_COLUMN_NULL))==0
        && isSortingIndex(pParse,pWC->pMaskSet,pProbe,iCur,pOrderBy,nEq,&rev)

      ){
        wsFlags |= WHERE_ROWID_RANGE|WHERE_COLUMN_RANGE|WHERE_ORDERBY;
        wsFlags |= (rev ? WHERE_REVERSE : 0);
      }else{
        bSort = 1;
      }
    }







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static int isSortingIndex(
  Parse *pParse,          /* Parsing context */
  WhereMaskSet *pMaskSet, /* Mapping from table cursor numbers to bitmaps */
  Index *pIdx,            /* The index we are testing */
  int base,               /* Cursor number for the table to be sorted */
  ExprList *pOrderBy,     /* The ORDER BY clause */
  int nEqCol,             /* Number of index columns with == constraints */
  int wsFlags,            /* Index usages flags */
  int *pbRev              /* Set to 1 if ORDER BY is DESC */
){
  int i, j;                       /* Loop counters */
  int sortOrder = 0;              /* XOR of index and ORDER BY sort direction */
  int nTerm;                      /* Number of ORDER BY terms */
  struct ExprList_item *pTerm;    /* A term of the ORDER BY clause */
  sqlite3 *db = pParse->db;
................................................................................
  *pbRev = sortOrder!=0;
  if( j>=nTerm ){
    /* All terms of the ORDER BY clause are covered by this index so
    ** this index can be used for sorting. */
    return 1;
  }
  if( pIdx->onError!=OE_None && i==pIdx->nColumn
      && (wsFlags & WHERE_COLUMN_NULL)==0
      && !referencesOtherTables(pOrderBy, pMaskSet, j, base) ){
    /* All terms of this index match some prefix of the ORDER BY clause
    ** and the index is UNIQUE and no terms on the tail of the ORDER BY
    ** clause reference other tables in a join.  If this is all true then
    ** the order by clause is superfluous.  Not that if the matching
    ** condition is IS NULL then the result is not necessarily unique
    ** even on a UNIQUE index, so disallow those cases. */
    return 1;
  }
  return 0;
}

/*
** Prepare a crude estimate of the logarithm of the input value.
................................................................................
    }

    /* If there is an ORDER BY clause and the index being considered will
    ** naturally scan rows in the required order, set the appropriate flags
    ** in wsFlags. Otherwise, if there is an ORDER BY clause but the index
    ** will scan rows in a different order, set the bSort variable.  */
    if( pOrderBy ){
      if( (wsFlags & WHERE_COLUMN_IN)==0
        && isSortingIndex(pParse, pWC->pMaskSet, pProbe, iCur, pOrderBy,
                          nEq, wsFlags, &rev)
      ){
        wsFlags |= WHERE_ROWID_RANGE|WHERE_COLUMN_RANGE|WHERE_ORDERBY;
        wsFlags |= (rev ? WHERE_REVERSE : 0);
      }else{
        bSort = 1;
      }
    }

Changes to test/tkt3824.test.

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    SELECT a FROM t2 WHERE b=2 AND c IS NULL ORDER BY b, a;
  }
} {5 9 sort}
do_test tkt3824-2.3 {
  lsort [execsql_status {
    SELECT a FROM t2 WHERE b=2 AND c IS NULL ORDER BY b;
  }]
} {5 9 sort}

do_test tkt3824-3.1 {
  db eval {
    CREATE TABLE t3(x,y);
    INSERT INTO t3 SELECT a, b FROM t1;
    INSERT INTO t3 VALUES(234,567);
    CREATE UNIQUE INDEX t3y ON t3(y);







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    SELECT a FROM t2 WHERE b=2 AND c IS NULL ORDER BY b, a;
  }
} {5 9 sort}
do_test tkt3824-2.3 {
  lsort [execsql_status {
    SELECT a FROM t2 WHERE b=2 AND c IS NULL ORDER BY b;
  }]
} {5 9 nosort}

do_test tkt3824-3.1 {
  db eval {
    CREATE TABLE t3(x,y);
    INSERT INTO t3 SELECT a, b FROM t1;
    INSERT INTO t3 VALUES(234,567);
    CREATE UNIQUE INDEX t3y ON t3(y);