Question

I have a very simple query which really needs to be as fast as possible…

The query is:

select users.userid, users.firstname, users.lastname
       from users_table users   
       where userid IN(1,4,6)

userid set as the primary key…

EXPLAIN returns the following:

id  |select_type|table|type |possible_keys|key    |key_len|ref |rows|Extra
1   |SIMPLE     |users|range|PRIMARY      |PRIMARY|4      |NULL|3   |Using where

Now, I was under the impression that ‘Using where’ is a bad thing?

Can anybody explain why I might be seeing this?

Answer 1

In your query, the where is the only thing it can use. It looks like it’s using a primary key due to the IN clause being direct comparison to an indexed field (in this case your pk) so it don’t get much better than this! Actually, it’s impossible to get better than this…