Commit 9b5cf946 authored by unknown's avatar unknown
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A fix and test case for Bug#6088 "FOUND_ROWS returns wrong values for 

prepared statements when LIMIT is used" and post-review comments.
The fix changes the approach we calculate the need for ORDER BY 
in UNION: the previous was not PS friendly, as it damaged SELECT_LEX 
options in case of single select.


mysql-test/r/ps.result:
  Test results fixed: the test case for Bug#6088
mysql-test/r/subselect.result:
  Test results fixed: now we don't perform ORDER BY for parts of UNION
  if there is no LIMIT clause.
mysql-test/t/ps.test:
  A test case for Bug#6088 "FOUND_ROWS returns wrong values for
   prepared statements when LIMIT is used".
sql/sql_union.cc:
  The actual fix for Bug#6088:
  - don't modify SELECT_LEX'es
  - use boolean variable can_skip_order_by to check if we can skip
    ORDER BY in UNION
parent 1cd249e0

mysql-test/r/ps.result

+24 −0
Original line number Diff line number Diff line
@@ -410,3 +410,27 @@ a a 
1.1	1.2

2.1	2.2

deallocate prepare stmt;

create table t1 (a int);

insert into t1 (a) values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);

prepare stmt from "select sql_calc_found_rows * from t1 limit 2";

execute stmt;

a

1

2

select found_rows();

found_rows()

10

execute stmt;

a

1

2

select found_rows();

found_rows()

10

execute stmt;

a

1

2

select found_rows();

found_rows()

10

mysql-test/r/subselect.result

+3 −3
Original line number Diff line number Diff line
@@ -176,17 +176,17 @@ a b 
a	b

1	7

2	7

3	8

4	8

3	8

explain extended (select * from t2 where t2.b=(select a from t3 order by 1 desc limit 1)) union (select * from t4 where t4.b=(select max(t2.a)*4 from t2) order by a);

id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra

1	PRIMARY	t2	ALL	NULL	NULL	NULL	NULL	2	Using where

2	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	3	Using filesort

3	UNION	t4	ALL	NULL	NULL	NULL	NULL	3	Using where; Using filesort

3	UNION	t4	ALL	NULL	NULL	NULL	NULL	3	Using where

4	SUBQUERY	t2	ALL	NULL	NULL	NULL	NULL	2	

NULL	UNION RESULT	<union1,3>	ALL	NULL	NULL	NULL	NULL	NULL	

Warnings:

Note	1003	(select test.t2.a AS `a`,test.t2.b AS `b` from test.t2 where (test.t2.b = (select test.t3.a AS `a` from test.t3 order by test.t3.a desc limit 1))) union (select test.t4.a AS `a`,test.t4.b AS `b` from test.t4 where (test.t4.b = (select (max(test.t2.a) * 4) AS `max(t2.a)*4` from test.t2)) order by test.t4.a)

Note	1003	(select test.t2.a AS `a`,test.t2.b AS `b` from test.t2 where (test.t2.b = (select test.t3.a AS `a` from test.t3 order by test.t3.a desc limit 1))) union (select test.t4.a AS `a`,test.t4.b AS `b` from test.t4 where (test.t4.b = (select (max(test.t2.a) * 4) AS `max(t2.a)*4` from test.t2)) order by a)

select (select a from t3 where a<t2.a*4 order by 1 desc limit 1), a from t2;

(select a from t3 where a<t2.a*4 order by 1 desc limit 1)	a

3	1

mysql-test/t/ps.test

+14 −0
Original line number Diff line number Diff line
@@ -415,3 +415,17 @@ execute stmt; 
execute stmt;

execute stmt;

deallocate prepare stmt;



#

# Bug#6088 "FOUND_ROWS returns wrong values for prepared statements when

# LIMIT is used"

# 

create table t1 (a int);

insert into t1 (a) values (1), (2), (3), (4), (5), (6), (7), (8), (9), (10);

prepare stmt from "select sql_calc_found_rows * from t1 limit 2";

execute stmt;

select found_rows();

execute stmt;

select found_rows();

execute stmt;

select found_rows();

sql/sql_union.cc

+13 −15
Original line number Diff line number Diff line
@@ -147,6 +147,7 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result, 
  SELECT_LEX *lex_select_save= thd_arg->lex->current_select;

  SELECT_LEX *sl, *first_select;

  select_result *tmp_result;

  bool is_union;

  DBUG_ENTER("st_select_lex_unit::prepare");



  describe= test(additional_options & SELECT_DESCRIBE);
@@ -183,10 +184,11 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result, 
  

  thd_arg->lex->current_select= sl= first_select= first_select_in_union();

  found_rows_for_union= first_select->options & OPTION_FOUND_ROWS;

  is_union= test(first_select->next_select());



  /* Global option */



  if (first_select->next_select())

  if (is_union)

  {

    if (!(tmp_result= union_result= new select_union(0)))

      goto err;
@@ -195,14 +197,11 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result, 
      tmp_result= sel_result;

  }

  else

  {

    tmp_result= sel_result;

    // single select should be processed like select in p[arantses

    first_select->braces= 1;

  }



  for (;sl; sl= sl->next_select())

  {

    bool can_skip_order_by;

    sl->options|=  SELECT_NO_UNLOCK;

    JOIN *join= new JOIN(thd_arg, sl->item_list, 

			 sl->options | thd_arg->options | additional_options,
@@ -218,13 +217,16 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result, 
    if (select_limit_cnt == HA_POS_ERROR || sl->braces)

      sl->options&= ~OPTION_FOUND_ROWS;



    can_skip_order_by= is_union &&

                       (!sl->braces || select_limit_cnt == HA_POS_ERROR);



    res= join->prepare(&sl->ref_pointer_array,

		       (TABLE_LIST*) sl->table_list.first, sl->with_wild,

		       sl->where,

		       ((sl->braces) ? sl->order_list.elements : 0) +

                       (can_skip_order_by ? 0 : sl->order_list.elements) +

                       sl->group_list.elements,

		       (sl->braces) ? 

		       (ORDER *)sl->order_list.first : (ORDER *) 0,

                       can_skip_order_by ?

                       (ORDER*) 0 : (ORDER *)sl->order_list.first,

		       (ORDER*) sl->group_list.first,

		       sl->having,

		       (ORDER*) NULL,
@@ -264,10 +266,8 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result, 
    }

  }



  if (first_select->next_select())

  if (is_union)

  {

    /* This is not a single select */



    /*

      Check that it was possible to aggregate

      all collations together for UNION.
@@ -364,8 +364,6 @@ int st_select_lex_unit::prepare(THD *thd_arg, select_result *sel_result, 
      }

    }

  }

  else

    first_select->braces= 0; // remove our changes



  thd_arg->lex->current_select= lex_select_save;