JOIN problem

Hello I have 2 tables with two columns in each one (cloned tables) like this : ID int(6) UserName varchar(25) and i would like to select usernames from table1 that doesnt appear in table2 so i did this : SELECT a.UserName FROM table1 a RIGHT OUTER JOIN table2 b ON (a.UserName = b.username) and that wont work, as i saw from sql joint docs, using OUTER JOIN significate that we want to join the 2 tables where the inverse of (a.UserName=b.username) is, so it's equivalent of (a.UserName<>b.username) and the LEFT option is about to show the lines from the left side table wich is a (table1) in my query why didnt that work fine ? how to resolve it and is my view on sql joins is incorect ? thanks all