SQL - how to count unique combination of columns

Question

I\'m not sure if this is possible but I want to count the number of unique value in a table. I know to count the number of unique folderIDs I do:

select count(f         


        

Answer 1

This will give you the count of unique folderid and userid combinations:

SELECT count(*)
  FROM (
        SELECT DISTINCT
               folderid,
               userid
          FROM folder
);

Hope it helps...