SQLite

** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is reponsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.204 2006/02/01 02:45:02 drh Exp $
*/
#include "sqliteInt.h"

/*
** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
*/
#define BMS  (sizeof(Bitmask)*8)

    int j;                      /* For looping over FROM tables */
    Index *pBest = 0;           /* The best index seen so far */
    int bestFlags = 0;          /* Flags associated with pBest */
    int bestNEq = 0;            /* nEq associated with pBest */
    double lowestCost;          /* Cost of the pBest */
    int bestJ = 0;              /* The value of j */
    Bitmask m;                  /* Bitmask value for j or bestJ */
    int once = 0;               /* True when first table is seen */

    lowestCost = SQLITE_BIG_DBL;
    for(j=iFrom, pTabItem=&pTabList->a[j]; j<pTabList->nSrc; j++, pTabItem++){
      if( once && 
          ((pTabItem->jointype & (JT_LEFT|JT_CROSS))!=0
           || (j>0 && (pTabItem[-1].jointype & (JT_LEFT|JT_CROSS))!=0))
      ){
        break;
      }
      m = getMask(&maskSet, pTabItem->iCursor);
      if( (m & notReady)==0 ){
        if( j==iFrom ) iFrom++;
        continue;
      }
      cost = bestIndex(pParse, &wc, pTabItem, notReady,
                       (i==0 && ppOrderBy) ? *ppOrderBy : 0,
                       &pIdx, &flags, &nEq);
      if( cost<lowestCost ){
        once = 1;
        lowestCost = cost;
        pBest = pIdx;
        bestFlags = flags;
        bestNEq = nEq;
        bestJ = j;
      }





    }
    TRACE(("*** Optimizer choose table %d for loop %d\n", bestJ,
           pLevel-pWInfo->a));
    if( (bestFlags & WHERE_ORDERBY)!=0 ){
      *ppOrderBy = 0;
    }
    andFlags &= bestFlags;

# 2006 January 31
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the join reordering optimization
# in cases that include a LEFT JOIN.
#
# $Id: where3.test,v 1.1 2006/02/01 02:45:02 drh Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# The following is from ticket #1652.
#
# A comma join then a left outer join:  A,B left join C.
# Arrange indices so that the B table is chosen to go first.
# Also put an index on C, but make sure that A is chosen before C.
#
do_test where3-1.1 {
  execsql {
    CREATE TABLE t1(a, b);
    CREATE TABLE t2(p, q);
    CREATE TABLE t3(x, y);
    
    INSERT INTO t1 VALUES(111,'one');
    INSERT INTO t1 VALUES(222,'two');
    INSERT INTO t1 VALUES(333,'three');
    
    INSERT INTO t2 VALUES(1,111);
    INSERT INTO t2 VALUES(2,222);
    INSERT INTO t2 VALUES(4,444);
    CREATE INDEX t2i1 ON t2(p);
    
    INSERT INTO t3 VALUES(999,'nine');
    CREATE INDEX t3i1 ON t3(x);
    
    SELECT * FROM t1, t2 LEFT JOIN t3 ON q=x WHERE p=2 AND a=q;
  }
} {222 two 2 222 {} {}}


finish_test