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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Do not flatten a subquery which is the right term of a LEFT OUTER JOIN if the subquery contains a WHERE clause. Ticket #350. (CVS 1027)
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SHA1: dd8943e8583cf7ed3b662570a5607856fd246dac
User & Date: drh 2003-06-16 00:40:35
Context
2003-06-16
03:08
Add the %z format to the sqlite_mprintf() and related functions. (CVS 1028) check-in: eca1398e user: drh tags: trunk
00:40
Do not flatten a subquery which is the right term of a LEFT OUTER JOIN if the subquery contains a WHERE clause. Ticket #350. (CVS 1027) check-in: dd8943e8 user: drh tags: trunk
00:16
Preserve blank lines in the middle of SQL statements in the shell. Ticket #352 (CVS 1026) check-in: bcf5eeec user: drh tags: trunk
Changes
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Changes to src/select.c.

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**    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 1.140 2003/05/31 16:21:13 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.
................................................................................
**   (9)  The subquery does not use LIMIT or the outer query does not use
**        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.



**
** In this routine, the "p" parameter is a pointer to the outer query.
** The subquery is p->pSrc->a[iFrom].  isAgg is true if the outer query
** uses aggregates and subqueryIsAgg is true if the subquery uses aggregates.
**
** If flattening is not attempted, this routine is a no-op and returns 0.
** If flattening is attempted this routine returns 1.
................................................................................
  **         (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







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**    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 1.141 2003/06/16 00:40:35 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.
................................................................................
**   (9)  The subquery does not use LIMIT or the outer query does not use
**        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)  The subquery is not the right term of a LEFT OUTER JOIN or the
**        subquery has no WHERE clause.  (added by ticket #350)
**
** In this routine, the "p" parameter is a pointer to the outer query.
** The subquery is p->pSrc->a[iFrom].  isAgg is true if the outer query
** uses aggregates and subqueryIsAgg is true if the subquery uses aggregates.
**
** If flattening is not attempted, this routine is a no-op and returns 0.
** If flattening is attempted this routine returns 1.
................................................................................
  **         (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;
  }

  /* 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.
  */
  if( iFrom>0 && (pSrc->a[iFrom-1].jointype & JT_OUTER)!=0 
      && pSub->pWhere!=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

Changes to test/join.test.

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#    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 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







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#    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 1.10 2003/06/16 00:40:35 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 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 t9 LEFT JOIN (SELECT x, q FROM t10, t11 WHERE t10.y=t11.p)
         ON( a=x);
  }
} {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 {} {}}

# 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
# separate selects but with on using a subquery and the other calling
# the table directly.  Then connect the two SELECTs using an EXCEPT.
# Both queries should generate the same results so the answer should
# be an empty set.
#
do_test join-9.1 {
  execsql {
    BEGIN;
    CREATE TABLE t12(a,b);
    INSERT INTO t12 VALUES(1,11);
    INSERT INTO t12 VALUES(2,22);
    CREATE TABLE t13(b,c);
    INSERT INTO t13 VALUES(22,222);
    COMMIT;
    SELECT * FROM t12 NATURAL LEFT JOIN t13
      EXCEPT
      SELECT * FROM t12 NATURAL LEFT JOIN (SELECT * FROM t13 WHERE b>0);
  }
} {}
do_test join-9.2 {
  execsql {
    CREATE VIEW v13 AS SELECT * FROM t13 WHERE b>0;
    SELECT * FROM t12 NATURAL LEFT JOIN t13
      EXCEPT
      SELECT * FROM t12 NATURAL LEFT JOIN v13;
  }
} {}

finish_test