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Character Set Support Before MySQL 4.1
Prior to MySQL 4.1, data values in MySQL have no explicit character set. Instead, string constants and column values are interpreted with respect to the server's character set. By default, this is the character set selected when the server was built (usually latin1), but the built-in value can be overridden at runtime with the --default-character-set option. This is very simple but quite limiting. For example, you cannot have a table that stores values using different character sets for different columns.
The single-character-set model also can lead to index-related problems if you change the server's character set after having already created tables and loaded character data into them. These problems occur due to the fact that index values are stored in sorted order, with the order for character columns being determined by the collating sequence of the character set that happens to be in force at the time the index entries are created. Some character sets have different collating sequences than others, so if you load a table while the server is using one character set and then reconfigure the server to use a different set, it's possible that the index entries will no longer be in the correct order with respect to the collating sequence of the new character set. Worse, if you add new rows to the table, the index that was initially created using the sort order of the original character set will be updated using the order of the new set. Consequently, index-based queries may not work correctly.
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