comparing a variable to value in DB

I have a column in my DB named username and i am trying to compare a session ID called $username to the field in my DB called username. The way i had done it before was SELECT * from tablename WHERE Tablename.username == $username, but this does not seem to be working is there a better way to do this? Also, I would like to know how to tell if a field is blank. For example, if my SELECT statement comes back and there is no data in the username column how can i check for this? _________________________________________________________________ Send and receive Hotmail on your mobile device: http://mobile.msn.com