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 1.138 2003/05/06 20:35:16 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.

**
** 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, or
**        the subquery is not itself a join.  (Ticket #306)
**
**   (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

  assert( pSubSrc );
  if( pSubSrc->nSrc==0 ) return 0;
  if( (pSub->isDistinct || pSub->nLimit>=0) &&  (pSrc->nSrc>1 || isAgg) ){
     return 0;
  }
  if( (p->isDistinct || p->nLimit>=0) && subqueryIsAgg ) return 0;
  if( p->pOrderBy && pSub->pOrderBy ) return 0;

  /* 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.
  */
  if( pSubSrc->nSrc>1 && iFrom>0 && (pSrc->a[iFrom-1].jointype & JT_OUTER)!=0 ){
    return 0;
  }

  /* If we reach this point, it means flattening is permitted for the
  ** iFrom-th entry of the FROM clause in the outer query.
  */

  /* Move all of the FROM elements of the subquery into the
  ** the FROM clause of the outer query.  Before doing this, remember
  ** the cursor number for the original outer query FROM element in
  ** iParent.  The iParent cursor will never be used.  Subsequent code
  ** will scan expressions looking for iParent references and replace
  ** those references with expressions that resolve to the subquery FROM
  ** elements we are now copying in.
  */
  iParent = pSrc->a[iFrom].iCursor;
  {
    int nSubSrc = pSubSrc->nSrc;
    int jointype = pSrc->a[iFrom].jointype;

    if( pSrc->a[iFrom].pTab && pSrc->a[iFrom].pTab->isTransient ){
      sqliteDeleteTable(0, pSrc->a[iFrom].pTab);
    }
    sqliteFree(pSrc->a[iFrom].zName);
    sqliteFree(pSrc->a[iFrom].zAlias);
    if( nSubSrc>1 ){
      int extra = nSubSrc - 1;
      for(i=1; i<nSubSrc; i++){
        pSrc = sqliteSrcListAppend(pSrc, 0, 0);
      }
      p->pSrc = pSrc;
      for(i=pSrc->nSrc-1; i-extra>=iFrom; i--){
        pSrc->a[i] = pSrc->a[i-extra];
      }
    }
    for(i=0; i<nSubSrc; i++){
      pSrc->a[i+iFrom] = pSubSrc->a[i];
      memset(&pSubSrc->a[i], 0, sizeof(pSubSrc->a[i]));
    }
    pSrc->a[iFrom+nSubSrc-1].jointype = jointype;
  }

  /* Now begin substituting subquery result set expressions for 
  ** references to the iParent in the outer query.
  ** 
  ** Example:
  **

#    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 1.9 2003/05/06 20:35:17 drh Exp $

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

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

    INSERT INTO t8 VALUES (4, NULL);
    INSERT INTO t8 VALUES (130, "pa31");
    INSERT INTO t8 VALUES (131, "pa30");

    SELECT coalesce(t8.a,999) from t7 LEFT JOIN t8 on y=a;
  }
} {1 999 999 2 131 130 999}

# Make sure a left join where the right table is really a view that
# is itself a join works right.  Ticket #306.
#
do_test join-8.1 {
  execsql {
    BEGIN;
    CREATE TABLE t9(a INTEGER PRIMARY KEY, b);
    INSERT INTO t9 VALUES(1,11);
    INSERT INTO t9 VALUES(2,22);
    CREATE TABLE t10(x INTEGER PRIMARY KEY, y);
    INSERT INTO t10 VALUES(1,2);
    INSERT INTO t10 VALUES(3,3);    
    CREATE TABLE t11(p INTEGER PRIMARY KEY, q);
    INSERT INTO t11 VALUES(2,111);
    INSERT INTO t11 VALUES(3,333);    
    CREATE VIEW v10_11 AS SELECT x, q FROM t10, t11 WHERE t10.y=t11.p;
    COMMIT;
    SELECT * FROM t9 LEFT JOIN v10_11 ON( a=x );
  }
} {1 11 1 111 2 22 {} {}}
do_test join-8.2 {
  execsql {
    SELECT * FROM v10_11 LEFT JOIN t9 ON( a=x );
  }
} {1 111 1 11 3 333 {} {}}

finish_test