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  1. MariaDB Server
  2. MDEV-15704

Fix Item_param::basic_const_item() to return true for temporal bound values

    Details

    • Type: Bug
    • Status: Open (View Workflow)
    • Priority: Major
    • Resolution: Unresolved
    • Affects Version/s: 10.3
    • Fix Version/s: 10.4
    • Component/s: Data types
    • Labels:
      None

      Description

      There is an asymmetry for temporal data types in Item_param:

      bool Item_param::basic_const_item() const
      {
        DBUG_ASSERT(fixed || state == NO_VALUE);
        if (state == NO_VALUE ||
            (state == SHORT_DATA_VALUE && type_handler()->cmp_type() == TIME_RESULT))
          return FALSE;
        return TRUE;
      }
      

      Notice, unlike for other data types, basic_const_item() returns false for bound temporal values.

      The reason for this was probably because prior to 10.0 we didn't have Item_temporal_literal (and its descendants) so that Item_param::clone_item() could not return a basic constant for temporal values.
      Now this asymmetry can be fixed, so Item_param::clone_item() returns non-NULL values for all data types.

      This asymmetry affects negatively various aspects, for example, constant propagation may not work as efficient, as for other data types.

      Also, in this example:

      EXECUTE IMMEDIATE 'CREATE OR REPLACE TABLE t1 (a TIME DEFAULT ?)' USING TIME'10:10:10';
      

      the default value is stored in the FRM as an expression rather than a constant (its visible if one opens the frm in a text editor).

      For non-temporal data types, Item_param used in DEFAULT clause is converted to constants, e.g.:

      EXECUTE IMMEDIATE 'CREATE OR REPLACE TABLE t1 (a INT DEFAULT ?)' USING 10;
      

      In this example, the default integer value 10 is stored in the FRM as an expression rather than a constant.

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

                • Created:
                  Updated: