MySQL: Converting Character set fails

MySQL

I'm in the progress of migrating my database from latin1 to utf8 character sets/collations.

I wrote a simple script that loops through all of my tables and executes this statement:

ALTER TABLE {database}.{table} CONVERT TO CHARACTER SET utf8 COLLATE utf8_unicode_ci;

This works great for almost all of the tables, but I noticed there are a few tables that fail to convert – the ALTER reports successful and there were no errors, but the collation remains as latin1.

Upon further inspection, I noticed that this particular table only has Integer columns, so perhaps this is the reason? But shouldn't that still at least change the table collation in the event I add VARCHARs later?

** edit **

I used phpMyAdmin's UI to convert the table and it gave me a slightly different command:

ALTER TABLE {table} DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci

What is the difference between these to statements; why would one work and not the other?

Best Answer

The ALTER TABLE ... DEFAULT CHARACTER SET ... command sets the default character set and collation for the table. It does not affect the existing VARCHAR/TEXT columns and their data. Only newly created fields will use the specified charset and collation.

The ALTER TABLE ... CONVERT TO CHARACTER SET ... command changes the character sets and collations of all the existing VARCHAR/TEXT fields (and converts the data). It actually should change the default charset for the table as well. It is not specified obvious enough here: http://dev.mysql.com/doc/refman/5.5/en/alter-table.html but it works in that way. On my MySQL 5.1.45 the default charset is changed by the CONVERT operation even it does not include VARCHAR-fields. Also the CONVERT operation may change the datatype if it cannot store the new length of data.

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