Hi ewrybody!!!

From a Selewct distinct statment in a database relation when i want to select only one type of expresion i get back null rezult.
exemple
select distinct col1, coln
form table1 table2 table3 table x
where colx = "component name.text"
the return rezult is null
The query is working because i get back the rezulted colums but the data in the rows are blank.
Working with Ibase
Sombogy somme ideea???