logical OR on two fields in a table in a database

[Erin ONeill]

Hey all!
I'm working on optimizing MySQL and in looking at the slow query log I have a pretty typical and basic query that is doing a FULL table scan -- even though both fields have indexes on them.

What I want to do is see if the variable is equal to either a Username or Email in one TABLE - no table joins here. This is for logging into the site. So the query looks something like this:
Select Username, Email where Username = $user OR Email = $user;

I just want a true or false, I don't really need the username or email.

The table is really large and only going to get larger. Not sure of the syntax for using IN, when I want to test TWO fields??

This doesn't seem to be discussed in optimizing queries (which all use ONE field when discussing the logical OR). I keep reading that the logical OR should be avoided. And let me tell you -- this query is a HOG and too slow!

Any suggestions?

erin