[MDEV-8723] Wrong result for SELECT..WHERE COLLATION(a)='binary' AND a='a' Created: 2015-09-01  Updated: 2015-09-12  Resolved: 2015-09-02

Status: Closed
Project: MariaDB Server
Component/s: Optimizer
Affects Version/s: 10.0, 10.1
Fix Version/s: 10.1.7

Type: Bug Priority: Major
Reporter: Alexander Barkov Assignee: Alexander Barkov
Resolution: Fixed Votes: 0
Labels: propagation, upstream-not-supported

Issue Links:
Blocks
blocks MDEV-8728 Fix a number of problems in equal fie... Closed
Relates
relates to MDEV-8695 Wrong result for SELECT..WHERE varcha... Closed

 Description   

In this script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARBINARY(10));
 
INSERT INTO t1 VALUES ('a');
 
SELECT * FROM t1 WHERE COLLATION(a)='binary';
 
SELECT * FROM t1 WHERE a='a';

the two SELECT queries return one row.

Now if I join both conditions using AND in the same query:

SELECT * FROM t1 WHERE COLLATION(a)='binary' AND a='a';

It returns empty set.

A similar script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARBINARY(10));
 
INSERT INTO t1 VALUES ('a');
 
SELECT * FROM t1 WHERE CHARSET(a)='binary';
 
SELECT * FROM t1 WHERE a='a'; 
SELECT * FROM t1 WHERE CHARSET(a)='binary' AND a='a';

A similar script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARBINARY(10));
 
INSERT INTO t1 VALUES ('a');
 
SELECT * FROM t1 WHERE COERCIBILITY(a)=2;
 
SELECT * FROM t1 WHERE a='a'; 
SELECT * FROM t1 WHERE COERCIBILITY(a)=2 AND a='a';

A similar script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARBINARY(10));
 
INSERT INTO t1 VALUES ('a');
 
SELECT * FROM t1 WHERE WEIGHT_STRING(a)='a';
 
SELECT * FROM t1 WHERE a='a'; 
SELECT * FROM t1 WHERE WEIGHT_STRING(a)='a' AND a='a';



 Comments   
Comment by Alexander Barkov [ 2015-09-12 ]

After the fix

EXPLAIN EXTENDED SELECT * FROM t1 WHERE COLLATION(a)='binary' AND a='a';
 
SHOW WARNINGS;

returns

+-------+------+------------------------------------------------------------------------------+
 
| Level | Code | Message                                                                      |
 
+-------+------+------------------------------------------------------------------------------+
 
| Note  | 1003 | select `test`.`t1`.`a` AS `a` from `test`.`t1` where (`test`.`t1`.`a` = 'a') |
 
+-------+------+------------------------------------------------------------------------------+

MySQL-5.7.8 does not support propagation in the same query:

+---------+------+-------------------------------------------------------------------------------------------------------------------------------------------+
 
| Level   | Code | Message                                                                                                                                   |
 
+---------+------+-------------------------------------------------------------------------------------------------------------------------------------------+
 
| Note    | 1003 | /* select#1 */ select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 'a') and (collation(`test`.`t1`.`a`) = 'binary')) |
 
+---------+------+-------------------------------------------------------------------------------------------------------------------------------------------+

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