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  1. MariaDB Server
  2. MDEV-30257

Value changed after adding DISTINCT [10.3.12, 10.11.1]

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

      SELECT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql1
      SELECT DISTINCT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql2
      

      However, the value -200412310000 changed to -2147483648 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 (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql1
      +---------------+
      | f1            |
      +---------------+
      | -200412310000 |
      +---------------+
      1 row in set (0.00 sec)
       
      mysql> SELECT DISTINCT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql2
      +-------------+
      | f1          |
      +-------------+
      | -2147483648 |
      +-------------+
      1 row in set (0.00 sec)
      

      How to repeat:

      drop table if exists t;
      CREATE TABLE t (c1 DECIMAL(40,20));
      INSERT INTO t VALUES (-0.0001);
       
      SELECT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql1
      SELECT DISTINCT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql2
      

      Hope these can be helpful for your debugging:
      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:10.3.12, it cannot be reproduced in mariadb:10.3.11:

      MariaDB [TEST]> select version();
      +----------------------------------------+
      | version()                              |
      +----------------------------------------+
      | 10.3.12-MariaDB-1:10.3.12+maria~bionic |
      +----------------------------------------+
      1 row in set (0.000 sec)
       
      MariaDB [TEST]> SELECT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql1
      +---------------+
      | f1            |
      +---------------+
      | -200412310000 |
      +---------------+
      1 row in set (0.000 sec)
       
      MariaDB [TEST]> SELECT DISTINCT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql2
      +-------------+
      | f1          |
      +-------------+
      | -2147483648 |
      +-------------+
      1 row in set (0.000 sec)
       
      MariaDB [TEST]> select version();
      +----------------------------------------+
      | version()                              |
      +----------------------------------------+
      | 10.3.11-MariaDB-1:10.3.11+maria~bionic |
      +----------------------------------------+
      1 row in set (0.000 sec)
       
      MariaDB [TEST]> SELECT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql1
      +---------------+
      | f1            |
      +---------------+
      | -200412310000 |
      +---------------+
      1 row in set (0.000 sec)
       
      MariaDB [TEST]> SELECT DISTINCT (LAST_DAY('2004-12-20 21:48:16') DIV c1) AS f1 FROM t; -- sql2
      +---------------+
      | f1            |
      +---------------+
      | -200412310000 |
      +---------------+
      1 row in set (0.000 sec)
      

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              bar Alexander Barkov
              qaqcatz qaqcatz
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