[MDEV-8793] Wrong result set for SELECT ... WHERE COALESCE(time_column)=TIME('00:00:00') AND COALESCE(time_column)=DATE('2015-09-11') - JIRA

Details

Type: Bug
Status: Closed
Priority: Major
Resolution: Fixed
Affects Version/s: 10.1, 10.0
Fix Version/s: 10.1.8
Component/s: Optimizer, Temporal Types
Labels:
- propagation

Description

SET timestamp=UNIX_TIMESTAMP('2015-09-11 20:20:20');
DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a TIME);
INSERT INTO t1 VALUES('10:20:30'),('00:00:00');
SELECT * FROM t1 WHERE COALESCE(a)=TIME('00:00:00');
SELECT * FROM t1 WHERE COALESCE(a)=DATE('2015-09-11');
SELECT * FROM t1 WHERE COALESCE(a)=TIME('00:00:00') AND COALESCE(a)=DATE('2015-09-11');

The first and the second SELECT query correctly return one row:

+----------+
| a        |
+----------+
| 00:00:00 |
+----------+

The third query erroneously returns empty set.

EXPLAIN SELECT * FROM t1 WHERE COALESCE(a)=TIME('00:00:00') AND COALESCE(a)=DATE('2015-09-11');

returns:

+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | Extra            |
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+
|    1 | SIMPLE      | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL | Impossible WHERE |
+------+-------------+-------+------+---------------+------+---------+------+------+------------------+

The problem happens in Arg_comparator::datetime() called from propagate_cond_constants.
Arg_comparator tries to compare the TIME and the DATE literals and fails.

If I rewrite the query like this:

SELECT * FROM t1 WHERE COALESCE(a)=TIME'00:00:00' AND COALESCE(a)=DATE'2015-09-11';

it returns the correct row:

+----------+
| a        |
+----------+
| 00:00:00 |
+----------+

But equal expression propagation is not performed:

EXPLAIN EXTENDED SELECT * FROM t1 WHERE COALESCE(a)=TIME'00:00:00' AND COALESCE(a)=DATE'2015-09-11';
SHOW WARNINGS;

+-------+------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level | Code | Message                                                                                                                                                |
+-------+------+--------------------------------------------------------------------------------------------------------------------------------------------------------+
| Note  | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((coalesce(`test`.`t1`.`a`) = TIME'00:00:00') and (coalesce(`test`.`t1`.`a`) = DATE'2015-09-11')) |
+-------+------+--------------------------------------------------------------------------------------------------------------------------------------------------------+

which also looks like a bug.

Summary: both queries:

SELECT * FROM t1 WHERE COALESCE(a)=TIME('00:00:00') AND COALESCE(a)=DATE('2015-09-11');
SELECT * FROM t1 WHERE COALESCE(a)=TIME'00:00:00' AND COALESCE(a)=DATE'2015-09-11';

are expected to return one row, and perform equal expression propagation.

the first query performs propagation but returns a wrong result
the second query returns a correct result but does not perform propagation

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blocks

MDEV-8728 Fix a number of problems in equal field and equal expression propagation

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Alexander Barkov added a comment - 2015-09-13 15:36

MySQL-5.7.8 does not support equal expression propagation in this example:

EXPLAIN EXTENDED SELECT * FROM t1 WHERE COALESCE(a)=TIME('00:00:00') AND COALESCE(a)=DATE('2015-09-11');
SHOW WARNINGS;

returns

+---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Level   | Code | Message                                                                                                                                                               |
+---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Warning | 1681 | 'EXTENDED' is deprecated and will be removed in a future release.                                                                                                     |
| Note    | 1003 | /* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((coalesce(`test`.`t1`.`a`) = TIME'00:00:00') and (coalesce(`test`.`t1`.`a`) = DATE'2015-09-11')) |
+---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Show

Alexander Barkov added a comment - 2015-09-13 15:36 MySQL-5.7.8 does not support equal expression propagation in this example: EXPLAIN EXTENDED SELECT * FROM t1 WHERE COALESCE(a)=TIME('00:00:00') AND COALESCE(a)=DATE('2015-09-11'); SHOW WARNINGS; returns +---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Level | Code | Message | +---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Warning | 1681 | 'EXTENDED' is deprecated and will be removed in a future release. | | Note | 1003 | /* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((coalesce(`test`.`t1`.`a`) = TIME'00:00:00') and (coalesce(`test`.`t1`.`a`) = DATE'2015-09-11')) | +---------+------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------+

Wrong result set for SELECT ... WHERE COALESCE(time_column)=TIME('00:00:00') AND COALESCE(time_column)=DATE('2015-09-11')

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