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  1. MariaDB Server
  2. MDEV-5836

MySQL WL#6292 - Make TIMESTAMP columns nullable by default




      revno: 3690.68.37
      committer: Gopal Shankar <gopal.shankar@oracle.com>
      branch nick: mysql-trunk-wl6292-push
      timestamp: Thu 2012-06-21 08:27:40 +0530
        WL#6292 - Make TIMESTAMP columns nullable by default.
        This worklog implements new behavior for TIMESTAMP columns,
        defined by CREATE TABLE, ALTER TABLE and CREATE SELECT commands.
        This is in effort to make TIMESTAMP columns behavior to be
        more closer to SQL standard. The change in behavior is as
        described below,
        Current behavior:
          1) Unlike all the other types, TIMESTAMP columns which are not
             explicitly specified as NULLable automatically get NOT NULL
             as attribute.
          2) If the first TIMESTAMP column in table is not specified as
             NULLable and doesn't have explicit DEFAULT or ON UPDATE
             value specified it automatically gets DEFAULT NOW()
             ON UPDATE NOW() as attributes.
          3) All other TIMESTAMP columns which are not NULLable and
             don't have explicit default specified get '0' as default
             value and treated as having explicit default value after
             that (i.e. if you don't provide explicit value for such
             a column when inserting into table no warning or error
             is emitted).
        New behavior:
          1) TIMESTAMP columns which are not explicitly specified as
             NOT NULL become NULLable.
          2) No TIMESTAMP columns get DEFAULT NOW() or ON UPDATE NOW()
             attributes automatically, without them being explicitly
          3) Non-NULLable TIMESTAMP columns without explicit default
             value treated as having no default value. I.e. warning
             or error is emitted (depends on sql_mode) if we insert
             a row without providing and explicit value for such a
             column. In case when warning is emitted and not an
             error such a column will still get '0' if no explicit
             value was specified for it.
        A new command line option '--explicit_defaults_for_timestamp'
        is introduced for MySQL server to enable new behavior. The old
        behavior is kept as default, so that the existing applications
        assuming old semantics work without any changes.
        Replication slave applier thread is extended with new interface,
        such that the slave applies the logs with old behavior, if the
        logs are generated by master with older version than slave.
        MySQL system table definitions at scripts/* were updated,
        such that they work fine with old and new behavior with
        any change. MTR tests which use TIMESTAMP columns are also
        updated, such that the test works both in old and new
        behavior. This should help easy transition to new behavior
        going forward.
        This worklog addresses Bug#11762529 and Bug#13344629.


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