I have the next query that in my opinion is a valid one, but I keep getting error telling me that there is a proble on "WHERE em.p4 = ue.p3" - Unknown column 'ue.p3' in 'where clause'. This is the query: SELECT DISTINCT ue.p3 FROM table1 AS ue INNER JOIN table2 AS e ON ue.p3 = e.p3 WHERE EXISTS( SELECT 1 FROM ( SELECT (COUNT(*) >= 1) AS MinMutual FROM table4 AS smm WHERE smm.p1 IN ( SELECT sem.p3 FROM table3 AS sem INNER JOIN table2 AS em ON sem.p3 = em.p3 WHERE em.p4 = ue.p3 AND sem.type = 'friends' AND em.p2 = 'normal' ) AND smm.p5 IN ( 15000,15151 ) ) AS Mutual WHERE Mutual.MinMutual = TRUE) LIMIT 11 If I execute the sub-query which is inside the EXISTS function, everything is O.K. PLEASE HELP!