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  1. MariaDB ColumnStore
  2. MCOL-4721

CHAR(1) is not collation-aware for GROUP/DISTINCT

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    • Sprint:
      2021-7, 2021-8

      Description

      It seems the fix for MCOL-4065 was incomplete.
      There is a test in rowgroup/rowgroup.cpp which makes CHAR(1) go around the collation aware routines and perform the comparison always case sensitively:

               if (UNLIKELY(getColType(col) == execplan::CalpontSystemCatalog::VARCHAR ||
                            (getColType(col) == execplan::CalpontSystemCatalog::CHAR  && (colWidths[col] > 1)) ||
                            getColType(col) == execplan::CalpontSystemCatalog::TEXT))
               {
                   CHARSET_INFO* cs = getCharset(col);
      

      This script demonstrates the problem:

      DROP TABLE IF EXISTS t1;
      CREATE TABLE t1 (a CHAR(1) CHARACTER SET latin1) ENGINE=ColumnStore;
      INSERT INTO t1 VALUES ('a'),('A');
      SELECT a, COUNT(*) FROM t1 GROUP BY a;
      

      +------+----------+
      | a    | COUNT(*) |
      +------+----------+
      | a    |        1 |
      | A    |        1 |
      +------+----------+
      

      SELECT DISTINCT a FROM t1;
      

      +------+
      | a    |
      +------+
      | a    |
      | A    |
      +------+
      

      The above results are wrong: 'A' and 'a' are equal values in latin1_swedish_ci. Both queries should return one row.

      The expected results are:

      DROP TABLE IF EXISTS t1;
      CREATE TABLE t1 (a CHAR(1) CHARACTER SET latin1) ENGINE=MyISAM;
      INSERT INTO t1 VALUES ('a'),('A');
      SELECT a, COUNT(*) FROM t1 GROUP BY a;
      

      +------+----------+
      | a    | COUNT(*) |
      +------+----------+
      | a    |        2 |
      +------+----------+
      

      SELECT DISTINCT a FROM t1;
      

      +------+
      | a    |
      +------+
      | a    |
      +------+
      

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              Assignee:
              bar Alexander Barkov
              Reporter:
              bar Alexander Barkov
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                Updated:
                Resolved:

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