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Description:
In theory, the result of sql2(DISTINCT) ⊆ the result of sql1:
(SELECT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1'); -- sql1
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(SELECT DISTINCT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1'); -- sql2
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However, the value 0 changed to 0.0 after adding DISTINCT, seems like a logical bug:
mysql> select version();
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+-----------------------------------------+
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| version() |
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+-----------------------------------------+
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| 10.11.1-MariaDB-1:10.11.1+maria~ubu2204 |
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+-----------------------------------------+
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1 row in set (0.00 sec)
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mysql> (SELECT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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+----------------+
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| (c1 DIV 1)*0.1 |
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+----------------+
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| 0 |
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| 1 |
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+----------------+
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2 rows in set (0.00 sec)
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mysql> (SELECT DISTINCT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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+----------------+
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| (c1 DIV 1)*0.1 |
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+----------------+
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| 0.0 |
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| 1 |
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+----------------+
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2 rows in set (0.00 sec)
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How to repeat:
drop table if exists t;
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create table t (c1 double);
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insert into t values (0.1);
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(SELECT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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(SELECT DISTINCT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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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:10.1.37, it cannot be reproduced in mariadb:10.1.36:
MariaDB [TEST]> select version();
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+--------------------------+
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| version() |
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+--------------------------+
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| 10.1.37-MariaDB-1~bionic |
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+--------------------------+
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1 row in set (0.00 sec)
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MariaDB [TEST]> (SELECT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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+----------------+
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| (c1 DIV 1)*0.1 |
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+----------------+
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| 0 |
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| 1 |
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+----------------+
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2 rows in set (0.00 sec)
|
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MariaDB [TEST]> (SELECT DISTINCT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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+----------------+
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| (c1 DIV 1)*0.1 |
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+----------------+
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| 0.0 |
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| 1 |
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+----------------+
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2 rows in set (0.00 sec)
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MariaDB [TEST]> select version();
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+--------------------------+
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| version() |
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+--------------------------+
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| 10.1.36-MariaDB-1~bionic |
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+--------------------------+
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1 row in set (0.00 sec)
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MariaDB [TEST]> (SELECT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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+----------------+
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| (c1 DIV 1)*0.1 |
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+----------------+
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| 0.0 |
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| 1 |
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+----------------+
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2 rows in set (0.00 sec)
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MariaDB [TEST]> (SELECT DISTINCT (c1 DIV 1)*0.1 FROM t) UNION ALL (SELECT '1');
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+----------------+
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| (c1 DIV 1)*0.1 |
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+----------------+
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| 0.0 |
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| 1 |
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+----------------+
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2 rows in set (0.00 sec)
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