SQLite

**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.465 2008/08/14 00:19:49 drh Exp $
*/
#include "sqliteInt.h"


/*
** Delete all the content of a Select structure but do not deallocate
** the select structure itself.

**
** Flattening is only attempted if all of the following are true:
**
**   (1)  The subquery and the outer query do not both use aggregates.
**
**   (2)  The subquery is not an aggregate or the outer query is not a join.
**
**   (3)  The subquery is not the right operand of a left outer join
**        (Originally ticket #306.  Strenghtened by ticket #3300)
**
**   (4)  The subquery is not DISTINCT or the outer query is not a join.
**
**   (5)  The subquery is not DISTINCT or the outer query does not use
**        aggregates.
**
**   (6)  The subquery does not use aggregates or the outer query is not

**        aggregates.
**
**  (10)  The subquery does not use aggregates or the outer query does not
**        use LIMIT.
**
**  (11)  The subquery and the outer query do not both have ORDER BY clauses.
**
**  (12)  Not implemented.  Subsumed into restriction (3).  Was previously
**        a separate restriction deriving from ticket #350.
**
**  (13)  The subquery and outer query do not both use LIMIT
**
**  (14)  The subquery does not use OFFSET
**
**  (15)  The outer query is not part of a compound select or the
**        subquery does not have both an ORDER BY and a LIMIT clause.

  }
  if( p->isDistinct && subqueryIsAgg ) return 0;         /* Restriction (6)  */
  if( (p->disallowOrderBy || p->pOrderBy) && pSub->pOrderBy ){
     return 0;                                           /* Restriction (11) */
  }
  if( isAgg && pSub->pOrderBy ) return 0;                /* Restriction (16) */

  /* OBSOLETE COMMENT 1:
  ** Restriction 3:  If the subquery is a join, make sure the subquery is 
  ** not used as the right operand of an outer join.  Examples of why this
  ** is not allowed:
  **
  **         t1 LEFT OUTER JOIN (t2 JOIN t3)
  **
  ** If we flatten the above, we would get
  **
  **         (t1 LEFT OUTER JOIN t2) JOIN t3
  **
  ** which is not at all the same thing.
  **



  ** OBSOLETE COMMENT 2:
  ** Restriction 12:  If the subquery is the right operand of a left outer
  ** join, make sure the subquery has no WHERE clause.
  ** An examples of why this is not allowed:
  **
  **         t1 LEFT OUTER JOIN (SELECT * FROM t2 WHERE t2.x>0)
  **
  ** If we flatten the above, we would get
  **
  **         (t1 LEFT OUTER JOIN t2) WHERE t2.x>0
  **
  ** But the t2.x>0 test will always fail on a NULL row of t2, which
  ** effectively converts the OUTER JOIN into an INNER JOIN.
  **
  ** THIS OVERRIDES OBSOLETE COMMENTS 1 AND 2 ABOVE:
  ** Ticket #3300 shows that flattening the right term of a LEFT JOIN
  ** is fraught with danger.  Best to avoid the whole thing.  If the
  ** subquery is the right term of a LEFT JOIN, then do not flatten.
  */
  if( (pSubitem->jointype & JT_OUTER)!=0 ){
    return 0;
  }

  /* Restriction 17: If the sub-query is a compound SELECT, then it must
  ** use only the UNION ALL operator. And none of the simple select queries
  ** that make up the compound SELECT are allowed to be aggregate or distinct
  ** queries.

#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.
#
# This file implements tests for joins, including outer joins.
#
# $Id: join.test,v 1.25 2008/08/14 00:19:49 drh Exp $

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

do_test join-1.1 {
  execsql {
    CREATE TABLE t1(a,b,c);

  } {1 11 1 111 2 22 {} {}}
}
do_test join-8.3 {
  execsql {
    SELECT * FROM v10_11 LEFT JOIN t9 ON( a=x );
  }
} {1 111 1 11 3 333 {} {}}
ifcapable subquery {
  # Constant expressions in a subquery that is the right element of a
  # LEFT JOIN evaluate to NULL for rows where the LEFT JOIN does not
  # match.  Ticket #3300
  do_test join-8.4 {
    execsql {
      SELECT * FROM t9 LEFT JOIN (SELECT 44, p, q FROM t11) AS sub1 ON p=a
    }
  } {1 11 {} {} {} 2 22 44 2 111}
}
} ;# ifcapable view

# Ticket #350 describes a scenario where LEFT OUTER JOIN does not
# function correctly if the right table in the join is really
# subquery.
#
# To test the problem, we generate the same LEFT OUTER JOIN in two