Question

I have say 5 tables,
user , t1, t2, t3, t4
user has a field called id.
t1 to t4 all have a corresponding field called user_id, and a field called verification.

Now I need to distinctly(or uniquely) select the user from user table, whose id exists at least once in at least one table among t1 to t4,and where the verification field is true.

Answer 1

From you detail description it looks that you are near solution. The EXISTS and OR need to be used (assuming that TRUE replaced with 1):

SELECT id FROM User u WHERE
    EXISTS(SELECT 1 FROM t1 WHERE u.id = t1.user_id AND t1.verification =1) 
    OR EXISTS(SELECT 1 FROM t2 WHERE u.id = t2.user_id AND t2.verification =1 )
    OR EXISTS(SELECT 1 FROM t3 WHERE u.id = t3.user_id AND t3.verification =1 ) 
    OR EXISTS(SELECT 1 FROM t4 WHERE u.id = t4.user_id AND t4.verification =1 )