Create an index on a MySQL column based on the length its contents?

问题

How do I create an index on a column in MySQL v 5.0 (myisam db engine) based upon the length of its value its a TEXT data type up to 7000 characters, do I have to add another column with the length of the first column?

回答1:

Yes, as MySQL doesn't support function-based indexes (like ADD INDEX myIndex(LENGTH(text))), you'll need a new int column and define a trigger to auto-update it after inserts and updates.

回答2:

Sounds like a good approach to me (sorry don't know mysql, but in oracle you could set a trigger so that when your main column is updated the "length" column gets automatically updated)

来源：https://stackoverflow.com/questions/84346/create-an-index-on-a-mysql-column-based-on-the-length-its-contents