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  1. MariaDB Server
  2. MDEV-6304

Controversial comparison behaviour of decimal literals with scale >30

        Details

        • Type: Bug
        • Status: Open
        • Priority: Minor
        • Resolution: Unresolved
        • Affects Version/s: 5.3.12, 5.5.37, 10.0.11
        • Fix Version/s: 10.1
        • Component/s: None
        • Labels:
          None

          Description

          Two decimal literals:
          0.1111111111222222222233333333334444444444
          and
          0.111111111122222222223333333333
          are considered as non-equal by "=",
          but considered as equal for UNION DISTINCT:

          MariaDB [test]> SELECT 0.1111111111222222222233333333334444444444 = 0.111111111122222222223333333333 AS cmp;
+-----+
| cmp |
+-----+
|   0 |
+-----+
1 row in set (0.00 sec)

MariaDB [test]> SELECT 0.1111111111222222222233333333334444444444 AS a UNION SELECT 0.111111111122222222223333333333;
+----------------------------------+
| a                                |
+----------------------------------+
| 0.111111111122222222223333333333 |
+----------------------------------+
1 row in set (0.01 sec)

          Comparison in "=" and comparison in UNION DISTINCT should use the same rules.

          The problem most likely happens because we don't support fields with decimal
          scale > 30. UNION uses a temporary table and creates a field,
          while '=' does not need a field and compares the two numbers directly.

          Literals should probably be fixed not to support more than 30 fractional as well.

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                  • Assignee:
                    bar Alexander Barkov
                    Reporter:
                    bar Alexander Barkov
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                    Dates

                    • Created:
                      Updated: