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  1. MariaDB Server
  2. MDEV-8257

Erroneous "Impossible where" when mixing decimal comparison and LIKE

        Details

        • Type: Bug
        • Status: Closed
        • Priority: Major
        • Resolution: Fixed
        • Affects Version/s: 10.1, 10.0
        • Fix Version/s: 10.1.5
        • Component/s: Optimizer
        • Labels:
          None

          Description

          This script:

          DROP TABLE IF EXISTS t1;
CREATE TABLE t1 (a DECIMAL(8,2));
INSERT INTO t1 VALUES (10);
SELECT * FROM t1 WHERE a=10.0;
SELECT * FROM t1 WHERE a LIKE 10.00;

          returns one row in both SELECT queries.

          Now if I join the two conditions into a single query:

          SELECT * FROM t1 WHERE a=10.0 AND a LIKE 10.00;

          it returns empty set.

          EXPLAIN tells that where condition is Impossible:

          MariaDB [test]> EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=10.0 AND a LIKE 10.00; 
+------+-------------+-------+------+---------------+------+---------+------+------+----------+------------------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra            |
+------+-------------+-------+------+---------------+------+---------+------+------+----------+------------------+
|    1 | SIMPLE      | NULL  | NULL | NULL          | NULL | NULL    | NULL | NULL |     NULL | Impossible WHERE |
+------+-------------+-------+------+---------------+------+---------+------+------+----------+------------------+

          The above is wrong.
          It seems that LIKE erroneously sets cmp_context for the arguments to DECIMAL_RESULT.
          It should set cmp_context either to STRING_RESULT or keep IMPOSSIBLE_RESULT.

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