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  1. MariaDB Server
  2. MDEV-6304

Controversial comparison behaviour of decimal literals with scale >30

    Details

    • Type: Bug
    • Status: Open (View Workflow)
    • 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
              • Votes:
                1 Vote for this issue
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                Dates

                • Created:
                  Updated: