SELECT alias1.a0 FROM (SELECT sub0.a0 FROM (SELECT A1 AS a0 FROM T2) sub1 JOIN (SELECT A AS a0 FROM T1) sub0 ON (sub0.a0 = sub1.a0) UNION ALL SELECT alias0.a0 FROM (SELECT sub2.a0 FROM (SELECT A AS a0 FROM T4) sub2 UNION ALL SELECT col0 AS a0 FROM T6 ) alias0 ) alias1;