Editing Unicode (section)

== Unicode and MySQL ==

Before 5.0 MySQL only supported [http://en.wikipedia.org/wiki/Iso-8859-1 iso-8859-1] (aka latin-1) character encodings.

=== Determining the current character set ===

To determine the character set MySQL is currently using execute this from the MySQL client:

 mysql> show create table version;
  *************************** 1. row ***************************
         Table: version
  Create Table: CREATE TABLE `version` (
    `version` varchar(255) default NULL
  ) ENGINE=MyISAM DEFAULT CHARSET=latin1
  1 row in set (0.00 sec)

In this case the database is set to latin1 (aka iso-8859-1).

=== What's actually stored ===

When EPrints stores utf-8 data in MySQL it is simply stored as bytes. For characters below code point 128 this doesn't make any difference (because the Unicode code points are the same as the iso-8859-1 equivalent). For code points above 128 multiple bytes will be stored in MySQL which, if viewed from a MySQL client, will look like this (in this case é):

 Ã©

When the data is read by EPrints it will use the raw bits as utf-8. So long as MySQL doesn't change the data coming in and out everything works correctly.

MySQL 5.0 and above support two Unicode encodings: utf-8 and ucs-2.

If MySQL is set to use utf-8 it will re-encode the utf-8 data sent from EPrints. For the "é" example above the data, when viewed in MySQL, will still look like:

 Ã©

But what MySQL has actually stored is:

 ÃƒÂ©