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Overview
Comment:If the cost of two whereLoop objects is the same in every way except that one has fewer expected output rows than the other, then choose the one with fewer output rows.
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SHA1:79e458ef7acfddbc189163e3e958da529becb130
User & Date: drh 2013-08-30 17:35:44
Context
2013-08-30
17:50
Fix comment typos in the where.c module. No code changes. check-in: 1e0b77cf user: drh tags: trunk
17:35
If the cost of two whereLoop objects is the same in every way except that one has fewer expected output rows than the other, then choose the one with fewer output rows. check-in: 79e458ef user: drh tags: trunk
14:24
Add the SQLITE_MINIMUM_FILE_DESCRIPTOR compile-time option, for control over exactly which low-numbered file descriptors SQLite will use. check-in: ba519053 user: drh tags: trunk
Changes
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Changes to src/where.c.

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    ** case first.  Hence compatible candidate WhereLoops never have a larger
    ** rSetup. Call this SETUP-INVARIANT */
    assert( p->rSetup>=pTemplate->rSetup );

    if( (p->prereq & pTemplate->prereq)==p->prereq
     && p->rSetup<=pTemplate->rSetup
     && p->rRun<=pTemplate->rRun

    ){
      /* This branch taken when p is equal or better than pTemplate in 
      ** all of (1) dependences (2) setup-cost, and (3) run-cost. */

      assert( p->rSetup==pTemplate->rSetup );
      if( p->nLTerm<pTemplate->nLTerm
       && (p->wsFlags & WHERE_INDEXED)!=0
       && (pTemplate->wsFlags & WHERE_INDEXED)!=0
       && p->u.btree.pIndex==pTemplate->u.btree.pIndex
       && p->prereq==pTemplate->prereq
      ){
................................................................................
        /* pTemplate is not helpful.
        ** Return without changing or adding anything */
        goto whereLoopInsert_noop;
      }
    }
    if( (p->prereq & pTemplate->prereq)==pTemplate->prereq
     && p->rRun>=pTemplate->rRun

     && ALWAYS(p->rSetup>=pTemplate->rSetup) /* See SETUP-INVARIANT above */
    ){
      /* Overwrite an existing WhereLoop with a better one: one that is
      ** better at one of (1) dependences, (2) setup-cost, or (3) run-cost
      ** and is no worse in any of those categories. */

      pNext = p->pNextLoop;
      break;
    }
  }

  /* If we reach this point it means that either p[] should be overwritten
  ** with pTemplate[] if p[] exists, or if p==NULL then allocate a new







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    ** case first.  Hence compatible candidate WhereLoops never have a larger
    ** rSetup. Call this SETUP-INVARIANT */
    assert( p->rSetup>=pTemplate->rSetup );

    if( (p->prereq & pTemplate->prereq)==p->prereq
     && p->rSetup<=pTemplate->rSetup
     && p->rRun<=pTemplate->rRun
     && p->nOut<=pTemplate->nOut
    ){
      /* This branch taken when p is equal or better than pTemplate in 
      ** all of (1) dependences (2) setup-cost, (3) run-cost, and
      ** (4) number of output rows. */
      assert( p->rSetup==pTemplate->rSetup );
      if( p->nLTerm<pTemplate->nLTerm
       && (p->wsFlags & WHERE_INDEXED)!=0
       && (pTemplate->wsFlags & WHERE_INDEXED)!=0
       && p->u.btree.pIndex==pTemplate->u.btree.pIndex
       && p->prereq==pTemplate->prereq
      ){
................................................................................
        /* pTemplate is not helpful.
        ** Return without changing or adding anything */
        goto whereLoopInsert_noop;
      }
    }
    if( (p->prereq & pTemplate->prereq)==pTemplate->prereq
     && p->rRun>=pTemplate->rRun
     && p->nOut>=pTemplate->nOut
     && ALWAYS(p->rSetup>=pTemplate->rSetup) /* See SETUP-INVARIANT above */
    ){
      /* Overwrite an existing WhereLoop with a better one: one that is
      ** better at one of (1) dependences, (2) setup-cost, (3) run-cost
      ** or (4) number of output rows, and is no worse in any of those
      ** categories. */
      pNext = p->pNextLoop;
      break;
    }
  }

  /* If we reach this point it means that either p[] should be overwritten
  ** with pTemplate[] if p[] exists, or if p==NULL then allocate a new

Changes to test/whereF.test.

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  3 {SELECT t1.a, t1.b, t2.d, t2.e FROM t2 CROSS JOIN t1 
     WHERE t2.d=t1.b AND t1.a=(t2.d+1) AND t1.b = (t2.e+1)}
} {
  do_test 3.$tn {
    db eval "EXPLAIN QUERY PLAN $sql"
   } {/.*SCAN TABLE t2\y.*SEARCH TABLE t1\y.*/}
}








finish_test








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  3 {SELECT t1.a, t1.b, t2.d, t2.e FROM t2 CROSS JOIN t1 
     WHERE t2.d=t1.b AND t1.a=(t2.d+1) AND t1.b = (t2.e+1)}
} {
  do_test 3.$tn {
    db eval "EXPLAIN QUERY PLAN $sql"
   } {/.*SCAN TABLE t2\y.*SEARCH TABLE t1\y.*/}
}

do_execsql_test 4.0 {
  CREATE TABLE t4(a,b,c,d,e, PRIMARY KEY(a,b,c));
  CREATE INDEX t4adc ON t4(a,d,c);
  CREATE UNIQUE INDEX t4aebc ON t4(a,e,b,c);
  EXPLAIN QUERY PLAN SELECT rowid FROM t4 WHERE a=? AND b=?;
} {/a=. AND b=./}

finish_test