Question

my request seems not so difficult but i am not sure about the best way to do it.

I have the following table:

userID  file
   1      1
   1      2 
   1      3
   2      1
   2      3
   3      2
   4      1
   4      2

And i would like to select UserID that only have the file number 2. In my example the result would be only 3.

Answer 1

SELECT userID
FROM tableName a
WHERE file = 2
GROUP BY userID
HAVING COUNT(*) = 
(
  SELECT COUNT(*)
  FROM tableName b
  WHERE a.userID = b.userID 
)

• SQLFiddle Demo