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We are considering to upgrade to MySQL 5.6 this summer. I would like to know if our data will be changed in any way once we perform the upgrade?

I've been reading and I found that mysql_upgrade upgrades the system tables only. I tested it and it seems to be true. But I just want to make sure that our data will remain the same after the upgrade. I don't want to have problems with our apps after we do the upgrade. Thanks!

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2 Answers 2

As noted, mysql_upgrade will change the system tables to include any new columns required.

MySQL 5.6 includes support for microseconds in DATETIME and TIMESTAMP, and as such uses a different format on disk for storage. Conversion to the new format does not happen as part of mysql_upgrade, but will happen on ALTER TABLE or OPTIMIZE TABLE and in which case you will not be able to start MySQL 5.5 and use this data directory.

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Mysql version upgrade will not make any changes to your stored data from your database! But as a best practice make sure you make a full backup for your database(dump + cold bkp) before you start the upgrade process.
Always have rollback plan

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True, except for the system tables, where there are structural changes, but there should be no data loss. Also, read the upgrade guide and all of the release notes for every release of MySQL 5.6 to verify that there are no incompatible changes that may cause issues if your application is relying on some behaviors of older versions that could have changed. –  Michael - sqlbot Mar 11 at 2:46

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