[MDEV-30252] Value changed after adding DISTINCT [5.5.62, 10.11.1] Created: 2022-12-17  Updated: 2023-11-28

Status: Confirmed
Project: MariaDB Server
Component/s: Optimizer
Affects Version/s: 5.5.62, 10.11.1
Fix Version/s: 10.4, 10.5, 10.6, 10.11

Type: Bug Priority: Major
Reporter: qaqcatz Assignee: Alexander Barkov
Resolution: Unresolved Votes: 0
Labels: datetime, distinct-optimization, subquery
Environment:

ubuntu 18.04


Issue Links:
Relates
relates to MDEV-30250 Value changed after relaxing ON condi... Confirmed

 Description   

Description:
In theory, the result of sql2(DISTINCT) ⊆ the result of sql1:

SELECT PI()+~1&f2 AS f1 FROM (SELECT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql1
SELECT PI()+~1&f2 AS f1 FROM (SELECT DISTINCT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql2

However, the value 20091014235959 changed to 2009 after adding DISTINCT, seems like a logical bug:

mysql> select version();
+-----------------------------------------+
| version()                               |
+-----------------------------------------+
| 10.11.1-MariaDB-1:10.11.1+maria~ubu2204 |
+-----------------------------------------+
1 row in set (0.00 sec)
 
mysql> SELECT PI()+~1&f2 AS f1 FROM (SELECT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql1
+----------------+
| f1             |
+----------------+
| 20091014235959 |
+----------------+
1 row in set, 1 warning (0.00 sec)
 
mysql> SELECT PI()+~1&f2 AS f1 FROM (SELECT DISTINCT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql2
+------+
| f1   |
+------+
| 2009 |
+------+
1 row in set, 2 warnings (0.00 sec)

How to repeat:

drop table if exists t;
CREATE TABLE t (c1 INT);
INSERT INTO t VALUES (1);
 
SELECT PI()+~1&f2 AS f1 FROM (SELECT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql1
SELECT PI()+~1&f2 AS f1 FROM (SELECT DISTINCT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql2

Hope these can be helpful for your debugging:
1. The bug cannot be reproduced after removing the date function (change to '2009-10-15' AS f2);
2. The bug cannot be reproduced after removing FROM t;
3. We look for the first version of the bug in all docker images (with format x.x.x) of https://hub.docker.com/_/mariadb/tags
We found that the bug first occurred in mariadb:5.5.62, it cannot be reproduced in mariadb:5.5.61:

MariaDB [TEST]> select version();
+-------------------------+
| version()               |
+-------------------------+
| 5.5.62-MariaDB-1~trusty |
+-------------------------+
1 row in set (0.00 sec)
 
MariaDB [TEST]> SELECT PI()+~1&f2 AS f1 FROM (SELECT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql1
+----------------+
| f1             |
+----------------+
| 20091014235959 |
+----------------+
1 row in set (0.00 sec)
 
MariaDB [TEST]> SELECT PI()+~1&f2 AS f1 FROM (SELECT DISTINCT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql2
+------+
| f1   |
+------+
| 2009 |
+------+
1 row in set, 1 warning (0.00 sec)
 
MariaDB [TEST]> select version();
+-------------------------+
| version()               |
+-------------------------+
| 5.5.61-MariaDB-1~trusty |
+-------------------------+
1 row in set (0.00 sec)
 
MariaDB [TEST]> SELECT PI()+~1&f2 AS f1 FROM (SELECT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql1
+------+
| f1   |
+------+
|    0 |
+------+
1 row in set (0.00 sec)
 
MariaDB [TEST]> SELECT PI()+~1&f2 AS f1 FROM (SELECT DISTINCT DATE_SUB(DATE_ADD('2009-10-15', INTERVAL 1 MICROSECOND), INTERVAL 1 DAY_SECOND) AS f2 FROM t) AS t1; -- sql2
+------+
| f1   |
+------+
|    0 |
+------+
1 row in set, 1 warning (0.00 sec)



 Comments   
Comment by Sergei Golubchik [ 2023-01-09 ]

Likely the same as MDEV-30250, let's retest after MDEV-30250 is fixed

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