SELECT * FROM (SELECT colA, colB FROM tableA UNION SELECT colA, colB FROM tableB) WHERE colA > 1 https://stackoverflow.com/questions/5437507/union-with-where-clause UNION with WHERE clause I'm doing a UNION of two queries on an Oracle database. Both of them have a WHERE clause. Is there a difference in the performance if I do the WHERE after UNIONing the queries compared to performin... stackove..