The MySQL 5.6.4 release introduced support for fractional values within the temporal datatypes: TIME, DATETIME, and TIMESTAMP. Hence the storage requirement and encoding differs for them in comparison to older (5.5 and earlier) temporal datatypes. The storage format for the temporal datatypes in the old format are not space efficient either, and recreating tables having both the new and old formats can be a long and tedious process. For these reasons, we wanted to make it easier for users to identify precisely which tables, if any, need to be upgraded.

In my previous blog post, where we looked at the process of upgrading old MySQL-5.5 format temporals to the MySQL-5.6 format, there was the …

The temporal datatypes ‘TIME/DATETIME/TIMESTAMP’ supports fractional values starting from MySQL 5.6.4 version. Hence the storage requirement and encoding differs in comparison to pre- MySQL 5.6.4 temporal datatypes.

As mentioned in the section ‘Upgrading from MySQL 5.5 to 5.6′,

http://dev.mysql.com/doc/refman/5.6/en/upgrading-from-previous-series.html

Once you have imported the pre-MySQL 5.6.4 tables, ‘ALTER TABLE’ allows creation of tables containing temporal columns of both mysql-5.5 and mysql-5.6 format.

As noted in the documentation, the disadvantages of having such tables are:

• Recreating tables having both 5.5 and 5.6 temporals becomes tedious process when the metadata file(.frm) for the table is unavailable. This would involve recreating the table having the old temporal columns using 5.5 server instance and then adding the 5.6 temporal columns using 5.6 server instance.
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