Does an additional "AND `columnname` LIKE '%'" hurt performance?

Question

simple question: Does adding something like this to a query hurt performance in mysql or does it quickly get optimized away?

AND `name` LIKE '%'

I've got no big database here that I could test it on.

By the way, I want this because I want users to be able to send some parameters to my server-side script that then grabs the prepared statement specified by the user and inserts the parameters. I want users to be able to omit parameters when searching without hurting the performance, and LIKE normally is relatively slow, right?

Answer 1

LIKE's can be expensive indeed, depending on the indexes you have on the name field. Have you tried to measure your query?

EXPLAIN [EXTENDED] SELECT [...] AND `name` LIKE '%'

See also http://dev.mysql.com/doc/refman/5.0/en/explain.html

Then MySQL will give you indications whether it has optimised the unnecessary LIKE clause away or not.