SQLite

    }
    sqlite3DebugPrintf("\n");
    for(ii=0; ii<pWInfo->nLevel; ii++){
      whereLoopPrint(pWInfo->a[ii].pWLoop, sWLB.pWC);
    }
  }
#endif

  /* Attempt to omit tables from the join that do not affect the result.
  ** For a table to not affect the result, the following must be true:
  **
  **   1) The query must not be an aggregate.
  **   2) The table must be the RHS of a LEFT JOIN.
  **   3) Either the query must be DISTINCT, or else the ON or USING clause
  **      must contain a constraint that limits the scan of the table to 
  **      at most a single row.
  **   4) The table must not be referenced by any part of the query apart
  **      from its own USING or ON clause.
  **
  ** For example, given:
  **
  **     CREATE TABLE t1(ipk INTEGER PRIMARY KEY, v1);
  **     CREATE TABLE t2(ipk INTEGER PRIMARY KEY, v2);
  **     CREATE TABLE t3(ipk INTEGER PRIMARY KEY, v3);
  **
  ** then table t2 can be omitted from the following:
  **
  **     SELECT v1, v3 FROM t1 
  **       LEFT JOIN t2 USING (t1.ipk=t2.ipk)
  **       LEFT JOIN t3 USING (t1.ipk=t3.ipk)
  **
  ** or from:
  **
  **     SELECT DISTINCT v1, v3 FROM t1 
  **       LEFT JOIN t2
  **       LEFT JOIN t3 USING (t1.ipk=t3.ipk)
  */
  if( pWInfo->nLevel>=2
   && pResultSet!=0               /* guarantees condition (1) above */
   && OptimizationEnabled(db, SQLITE_OmitNoopJoin)
  ){
    int i;
    Bitmask tabUsed = sqlite3WhereExprListUsage(pMaskSet, pResultSet);
    if( sWLB.pOrderBy ){
      tabUsed |= sqlite3WhereExprListUsage(pMaskSet, sWLB.pOrderBy);
    }
    for(i=pWInfo->nLevel-1; i>=1; i--){
      WhereTerm *pTerm, *pEnd;
      struct SrcList_item *pItem;
      pLoop = pWInfo->a[i].pWLoop;
      pItem = &pWInfo->pTabList->a[pLoop->iTab];
      if( (pItem->fg.jointype & JT_LEFT)==0 ) continue;
      if( (wctrlFlags & WHERE_WANT_DISTINCT)==0
       && (pLoop->wsFlags & WHERE_ONEROW)==0
      ){
        continue;
      }
      if( (tabUsed & pLoop->maskSelf)!=0 ) continue;
      pEnd = sWLB.pWC->a + sWLB.pWC->nTerm;
      for(pTerm=sWLB.pWC->a; pTerm<pEnd; pTerm++){
        if( (pTerm->prereqAll & pLoop->maskSelf)!=0 ){
          if( !ExprHasProperty(pTerm->pExpr, EP_FromJoin)
           || pTerm->pExpr->iRightJoinTable!=pItem->iCursor
          ){
            break;
          }
        }
      }
      if( pTerm<pEnd ) continue;
      WHERETRACE(0xffff, ("-> drop loop %c not used\n", pLoop->cId));
      if( i!=pWInfo->nLevel-1 ){
        int nByte = (pWInfo->nLevel-1-i) * sizeof(WhereLevel);
        memmove(&pWInfo->a[i], &pWInfo->a[i+1], nByte);
      }
      pWInfo->nLevel--;
      nTabList--;
    }
  }
  WHERETRACE(0xffff,("*** Optimizer Finished ***\n"));
  pWInfo->pParse->nQueryLoop += pWInfo->nRowOut;

    }
#endif
    if( pLevel->iLeftJoin ){
      int ws = pLoop->wsFlags;
      addr = sqlite3VdbeAddOp1(v, OP_IfPos, pLevel->iLeftJoin); VdbeCoverage(v);
      assert( (ws & WHERE_IDX_ONLY)==0 || (ws & WHERE_INDEXED)!=0 );
      if( (ws & WHERE_IDX_ONLY)==0 ){
        assert( pLevel->iTabCur==pTabList->a[pLevel->iFrom].iCursor );
        sqlite3VdbeAddOp1(v, OP_NullRow, pLevel->iTabCur);
      }
      if( (ws & WHERE_INDEXED) 
       || ((ws & WHERE_MULTI_OR) && pLevel->u.pCovidx) 
      ){
        sqlite3VdbeAddOp1(v, OP_NullRow, pLevel->iIdxCur);
      }
      if( pLevel->op==OP_Return ){

do_eqp_test 3.2 {
  SELECT v2 FROM t1 LEFT JOIN t2 USING (k2) LEFT JOIN t3_2 USING (k3);
} {
  0 0 0 {SCAN TABLE t1} 
  0 1 1 {SEARCH TABLE t2 USING INTEGER PRIMARY KEY (rowid=?)}
}

#-------------------------------------------------------------------------
# Test that tables other than the rightmost can be omitted from a
# LEFT JOIN query.
#
do_execsql_test 4.0 {
  CREATE TABLE c1(k INTEGER PRIMARY KEY, v1);
  CREATE TABLE c2(k INTEGER PRIMARY KEY, v2);
  CREATE TABLE c3(k INTEGER PRIMARY KEY, v3);

  INSERT INTO c1 VALUES(1, 2);
  INSERT INTO c2 VALUES(2, 3);
  INSERT INTO c3 VALUES(3, 'v3');

  INSERT INTO c1 VALUES(111, 1112);
  INSERT INTO c2 VALUES(112, 1113);
  INSERT INTO c3 VALUES(113, 'v1113');
}
do_execsql_test 4.1.1 {
  SELECT v1, v3 FROM c1 LEFT JOIN c2 ON (c2.k=v1) LEFT JOIN c3 ON (c3.k=v2);
} {2 v3 1112 {}}
do_execsql_test 4.1.2 {
  SELECT v1, v3 FROM c1 LEFT JOIN c2 ON (c2.k=v1) LEFT JOIN c3 ON (c3.k=v1+1);
} {2 v3 1112 {}}

do_execsql_test 4.1.3 {
  SELECT DISTINCT v1, v3 FROM c1 LEFT JOIN c2 LEFT JOIN c3 ON (c3.k=v1+1);
} {2 v3 1112 {}}

do_execsql_test 4.1.4 {
  SELECT v1, v3 FROM c1 LEFT JOIN c2 LEFT JOIN c3 ON (c3.k=v1+1);
} {2 v3 2 v3 1112 {} 1112 {}}

do_eqp_test 4.2.1 {
  SELECT v1, v3 FROM c1 LEFT JOIN c2 ON (c2.k=v1) LEFT JOIN c3 ON (c3.k=v2);
} {
  0 0 0 {SCAN TABLE c1} 
  0 1 1 {SEARCH TABLE c2 USING INTEGER PRIMARY KEY (rowid=?)}
  0 2 2 {SEARCH TABLE c3 USING INTEGER PRIMARY KEY (rowid=?)}
}
do_eqp_test 4.2.2 {
  SELECT v1, v3 FROM c1 LEFT JOIN c2 ON (c2.k=v1) LEFT JOIN c3 ON (c3.k=v1+1);
} {
  0 0 0 {SCAN TABLE c1} 
  0 1 2 {SEARCH TABLE c3 USING INTEGER PRIMARY KEY (rowid=?)}
}



finish_test