[MDEV-8747] Wrong result for SELECT..WHERE derived_table_column='a' AND derived_table_column<>_latin1'A' COLLATE latin1_bin Created: 2015-09-04  Updated: 2015-09-12  Resolved: 2015-09-06

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

Issue Links:
Blocks
blocks MDEV-8728 Fix a number of problems in equal fie... Closed
Relates
relates to MDEV-8749 Wrong result for SELECT..WHERE derive... Closed

 Description   

This script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARCHAR(10)) ENGINE=MyISAM;
 
INSERT INTO t1 VALUES ('a'),('A');
 
SELECT * FROM t1 WHERE a='a' AND a <> _latin1'A' COLLATE latin1_bin;

correctly returns one row:

+------+
 
| a    |
 
+------+
 
| a    |
 
+------+

If I rewrite the query to use a derived table:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARCHAR(10)) ENGINE=MyISAM;
 
INSERT INTO t1 VALUES ('a'),('A');
 
SELECT * FROM (SELECT * FROM t1) AS table1 WHERE a='a' AND a <> _latin1'A' COLLATE latin1_bin;

it erroneously returns two rows:

+------+
 
| a    |
 
+------+
 
| a    |
 
| A    |
 
+------+

The problems happens because Item_direct_view_ref has cmp_context correctly set to STRING_RESULT, while its referenced field has cmp_context set to IMPOSSIBLE_RESULT. This makes equal field propagation replace the field to constant in <>.

The same bug causes ENUM column to return bad results:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a ENUM('5','6')) ENGINE=MyISAM;
 
INSERT INTO t1 VALUES ('5'),('6');
 
SELECT * FROM (SELECT * FROM t1) AS table1 WHERE a='5';
 
SELECT * FROM (SELECT * FROM t1) AS table1 WHERE a=1;
 
SELECT * FROM (SELECT * FROM t1) AS table1 WHERE a='5' AND a=1;

The first and the second query correctly return one row, equal to '5'. The third query erroneously returns empty set.

The same problem is also demonstrated in this script:

DROP TABLE IF EXISTS t1;
 
DROP VIEW IF EXISTS v1;
 
CREATE TABLE t1 (a varchar(10) character set cp1251 collate cp1251_ukrainian_ci, KEY (a)) ;
 
INSERT INTO t1 VALUES ('DD'), ('ZZ'), ('ZZ'), ('KK'), ('FF'), ('HH'),('MM'),('`1');
 
CREATE VIEW v1 AS SELECT * FROM t1;
 
SELECT * FROM t1 WHERE a <> 0 AND a = ' 1';
 
SELECT * FROM v1 WHERE a <> 0 AND a = ' 1';

The first SELECT returns empty set, the second SELECT returns one row.

The same problem is repeatable in this script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a ENUM('5','6'));
 
INSERT INTO t1 VALUES ('5'),('6');
 
DROP VIEW IF EXISTS v1;
 
CREATE VIEW v1 AS SELECT * FROM t1;
 
SELECT * FROM t1 WHERE a='5' AND a<2;
 
SELECT * FROM v1 WHERE a='5' AND a<2;

The first SELECT correctly return one row, the second SELECT erroneously returns no rows.

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

MySQL-5.7.8 returns a wrong result for this script:

DROP TABLE IF EXISTS t1;
 
CREATE TABLE t1 (a VARCHAR(10)) ENGINE=MyISAM;
 
INSERT INTO t1 VALUES ('a'),('A');
 
SELECT * FROM t1 WHERE a='a' AND a <> _latin1'A' COLLATE latin1_bin;
 

+------+
 
| a    |
 
+------+
 
| a    |
 
| A    |
 
+------+

The correct result is to return one row only.

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