MySQL表索引

I have mysql tabel called 'users'. There are two obvious fields: 'user' and 'pass'.

My authentication query is like this:

"SELECT pass FROM users WHERE user = ? AND pass = ?"

I'd tought indexing could speed up the query. Should I index only 'user' field or also 'pass' field?

Also is comparing passwords with sql query faster than with PHP string compare.

First of all, you shouldn't be storing passwords in plain text. Store password hashes instead.

Second, index on either user or pass will help. But if you create a compound index on (user, pass), it will become a covering index for this query. This means that the query can be served directly from index, without consulting data files.