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  1. MariaDB Server
  2. MDEV-7005

NULLIF does not work as documented

        Details

        • Type: Bug
        • Status: Closed
        • Priority: Minor
        • Resolution: Fixed
        • Affects Version/s: 5.5.40, 10.0.14
        • Fix Version/s: 10.1.2
        • Component/s: Temporal Types
        • Labels:
          None

          Description

          The manual at https://mariadb.com/kb/en/mariadb/documentation/functions-and-operators/control-flow-functions/nullif/ says that NULLIF(expr1,expr2) is the same as CASE WHEN expr1 = expr2 THEN NULL ELSE expr1 END.
          In fact it is not always true.

          DROP TABLE IF EXISTS t1,t2;
CREATE TABLE t1 (a TIME);
CREATE TABLE t2 AS SELECT a,NULLIF(a,a), CASE WHEN a=a THEN NULL ELSE a END FROM t1;
SHOW CREATE TABLE t2;

          returns:

          +-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table                                                                                                                                                                           |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t2    | CREATE TABLE `t2` (
  `a` time DEFAULT NULL,
  `NULLIF(a,a)` varchar(10) DEFAULT NULL,
  `CASE WHEN a=a THEN NULL ELSE a END` time DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

          Notice, NULLIF erroneously created a VARCHAR column, while CASE correctly created a TIME column.

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