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  1. MariaDB Server
  2. MDEV-5994

MySQL WL#6292 - Make TIMESTAMP columns nullable by default




      Found while attempting to merge main.type_timestamp_explicit:

          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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              bar Alexander Barkov
              svoj Sergey Vojtovich
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