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Fix for Bug#14636211 WRONG RESULT (EXTRA ROW) ON A FROM SUBQUERY

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WITH A VARIABLE AND ORDER BY
        Bug#16035412 MYSQL SERVER 5.5.29 WRONG SORTING USING COMPLEX INDEX
      
This is a fix for a regression introduced by Bug#12667154:
Bug#12667154 attempted to fix a performance problem with subqueries
that did filesort. For doing filesort, the optimizer creates a quick
select object to use when building the sort index. This quick select
object was deleted after the first call to create_sort_index(). Thus,
for queries where the subquery was executed multiple times, the quick
object was only used for the first execution. For all later executions
of the subquery, filesort used a complete table scan for building the
sort index. The fix for Bug#12667154 tried to fix this by not deleting
the quick object after the first execution of create_sort_index() so
that it would be re-used for building the sort index by the following
executions of the subquery.
      
This regression introduced in Bug#12667154 is that due to not deleting
the quick select object after building the sort index, the quick
object could in some cases be used also during the second phase of the
execution of the subquery instead of using the created sort
index. This caused wrong results to be returned.
      
The fix for this issue is to delete the reference to the select object
after it has been used in create_sort_index(). In this way the select 
and quick objects will not be available when doing the second phase
of the execution of the select operation. To ensure that the select
object can be re-used for the following executions of the subquery
we make a copy of the select pointer. This is used for restoring the
select object after the select operation is completed.
This commit is contained in:
Olav Sandstaa
2013-01-14 10:58:17 +01:00
parent 18a9945c5b
commit e810f7f4eb
3 changed files with 54 additions and 14 deletions
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16
sql/sql_select.h
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@ -1,7 +1,7 @@
#ifndef SQL_SELECT_INCLUDED
#define SQL_SELECT_INCLUDED
/* Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
/* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
@ -160,6 +160,20 @@ typedef struct st_join_table {
TABLE *table;
KEYUSE *keyuse; /**< pointer to first used key */
SQL_SELECT *select;
/**
When doing filesort, the select object is used for building the
sort index. After the sort index is built, the pointer to the
select object is set to NULL to avoid that it is used when reading
the result records (@see create_sort_index()). For subqueries that
do filesort and that are executed multiple times, the pointer to
the select object must be restored before the next execution both
to ensure that the select object is used and to be able to cleanup
the select object after the final execution of the subquery. In
order to be able to restore the pointer to the select object, it
is saved in saved_select in create_sort_index() and restored in
JOIN::exec() after the main select is done.
*/
SQL_SELECT *saved_select;
COND *select_cond;
QUICK_SELECT_I *quick;
Item **on_expr_ref; /**< pointer to the associated on expression */