The UNION clause allows the results
of two queries to be combined. The second query is surrounded
by parentheses.
select * from java.lang.String union (select * from java.lang.StringBuilder)The two queries must match in the number of columns in the select clause.
SELECT s, s.value, s.hash FROM java.lang.String s UNION (SELECT b, b.value, "dummy" FROM java.lang.StringBuilder b )