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Bug#48920: COUNT DISTINCT returns 1 for NULL values when in a

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subquery in the select list
      
When a dependent subquery with count(distinct <col>) was 
evaluated multiple times, the Distinct_Aggregator was reused. 
However, the Aggregator was not reset, so when the subquery was
evaluated for the next record in the outer select, old dependent
info was used.
      
The fix is to clear() the existing aggregator in 
Item_sum::set_aggregator(). This ensures that the aggregator is
reevaluated with the new dependent information.

mysql-test/r/subselect3.result:
  Added test case for BUG#48920
mysql-test/t/subselect3.test:
  Added test case for BUG#48920
sql/item_sum.cc:
  If an aggregator exists when Item_sum::set_aggregator() is
  called (i.e., set_aggregator is called in a dependent
  subquery), the aggregator is reset so that the aggregator is
  reevaluated with the dependent information from the outer
  record being evaluated.
This commit is contained in:
Jorgen Loland 2010-01-04 10:39:42 +01:00
parent 1445cdaec8
commit 305f2e7f8a
3 changed files with 104 additions and 0 deletions
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50
mysql-test/r/subselect3.result
View file

@ -964,3 +964,53 @@ Variable_name Value
Handler_read_rnd_next 18
DROP TABLE t1,t2;
End of 5.1 tests
#
# BUG#48920: COUNT DISTINCT returns 1 for NULL values when in a subquery
# in the select list
#
CREATE TABLE t1 (
i int(11) DEFAULT NULL,
v varchar(1) DEFAULT NULL
);
INSERT INTO t1 VALUES (8,'v');
INSERT INTO t1 VALUES (9,'r');
INSERT INTO t1 VALUES (NULL,'y');
CREATE TABLE t2 (
i int(11) DEFAULT NULL,
v varchar(1) DEFAULT NULL,
KEY i_key (i)
);
INSERT INTO t2 VALUES (NULL,'r');
INSERT INTO t2 VALUES (0,'c');
INSERT INTO t2 VALUES (0,'o');
INSERT INTO t2 VALUES (2,'v');
INSERT INTO t2 VALUES (7,'c');
SELECT i, v, (SELECT COUNT(DISTINCT i)
FROM t1
WHERE v = t2.v) as subsel
FROM t2;
i v subsel
NULL r 1
0 c 0
0 o 0
2 v 1
7 c 0
EXPLAIN EXTENDED
SELECT i, v, (SELECT COUNT(DISTINCT i)
FROM t1
WHERE v = t2.v) as subsel
FROM t2;
id select_type table type possible_keys key key_len ref rows filtered Extra
1 PRIMARY t2 ALL NULL NULL NULL NULL 5 100.00
2 DEPENDENT SUBQUERY t1 ALL NULL NULL NULL NULL 3 100.00 Using where
Warnings:
Note 1276 Field or reference 'test.t2.v' of SELECT #2 was resolved in SELECT #1
Note 1003 select `test`.`t2`.`i` AS `i`,`test`.`t2`.`v` AS `v`,(select count(distinct `test`.`t1`.`i`) AS `COUNT(DISTINCT i)` from `test`.`t1` where (`test`.`t1`.`v` = `test`.`t2`.`v`)) AS `subsel` from `test`.`t2`
DROP TABLE t1,t2;
End of 5.6 tests

47
mysql-test/t/subselect3.test
View file

@ -794,3 +794,50 @@ SHOW STATUS LIKE '%Handler_read_rnd_next';
DROP TABLE t1,t2;
--echo End of 5.1 tests
--echo #
--echo # BUG#48920: COUNT DISTINCT returns 1 for NULL values when in a subquery
--echo # in the select list
--echo #
--echo
CREATE TABLE t1 (
i int(11) DEFAULT NULL,
v varchar(1) DEFAULT NULL
);
--echo
INSERT INTO t1 VALUES (8,'v');
INSERT INTO t1 VALUES (9,'r');
INSERT INTO t1 VALUES (NULL,'y');
--echo
CREATE TABLE t2 (
i int(11) DEFAULT NULL,
v varchar(1) DEFAULT NULL,
KEY i_key (i)
);
--echo
INSERT INTO t2 VALUES (NULL,'r');
INSERT INTO t2 VALUES (0,'c');
INSERT INTO t2 VALUES (0,'o');
INSERT INTO t2 VALUES (2,'v');
INSERT INTO t2 VALUES (7,'c');
--echo
SELECT i, v, (SELECT COUNT(DISTINCT i)
FROM t1
WHERE v = t2.v) as subsel
FROM t2;
--echo
EXPLAIN EXTENDED
SELECT i, v, (SELECT COUNT(DISTINCT i)
FROM t1
WHERE v = t2.v) as subsel
FROM t2;
DROP TABLE t1,t2;
--echo End of 5.6 tests

7
sql/item_sum.cc
View file

@ -578,7 +578,14 @@ int Item_sum::set_aggregator(Aggregator::Aggregator_type aggregator)
{
if (aggr)
{
/*
Dependent subselects may be executed multiple times, making
set_aggregator to be called multiple times. The aggregator type
will be the same, but it needs to be reset so that it is
reevaluated with the new dependent data.
*/
DBUG_ASSERT(aggregator == aggr->Aggrtype());
aggr->clear();
return FALSE;
}
switch (aggregator)