SQL: Selecting empty rows

Hi ! I got php4 and Postgresql 6.5. I created a fresh table with some fields, espacialy a text-field (lets call it "test"). I filled in about 10 rows. In 3 rows, I filled the field test with some text. What I want to do: 1.) Select all fields, where the field "test" is emtpy. 2.) Select all fields, where a string is NOT inside the field "test". I tried: select * from table where test=''; select * from table where test like ''; select * from table where test not like 'string'; But I never get any rows back, where the field "test" has not been set. Please help ! Regards Martin