I have a varchar(384) to store emails in a MyISAM table and I want check when the email exists but the index length limit is 333 bytes (because I'm using utf8 (1000 bytes/3 bytes)).
Then what's the best way to search if a specified email exists, using a FULLTEXT index or creating another field with the email md5-hash in a BINARY(16) (with collisions check)?
[EDIT]
Tests using 1M records.
Fulltext index: ~300 ms
333 length index: ~15 ms
binary(16) md5-hash: ~15 ms
So I think that the best option is the second field in performance, but... second field = bigger table, and that's not good for performance or storage. So in a real scenary where emails aren't bigger than 150 characters, a 150 length index in a VARCHAR(384) will be enough.