Select CAST(f1 AS DATATYPE1) F1, CAST(f2 AS DATATYPE2) F2, CAST(f3 AS DATATYPE3) F3 from table 1 union all Select CAST(f1 AS DATATYPE1) F1, CAST(f2 AS DATATYPE2) F2, CAST(f3 AS DATATYPE3) F3 from table 2