NOT EXIST clause

I am using the NOT EXIST clause in a select statement and it appears to not be working. I know that there is one record in table a that is not in table b and I though that it would give me that one record. SQL select * from test:a where NOT EXIST (select * from live:b) It returns with no records. I have noticed that this statement works on a table with less records in it. Does someone have a solution.