CREATE TABLE t1 (a VARCHAR(10), FULLTEXT KEY a (a));
INSERT INTO t1 VALUES (1),(2);
CREATE TABLE t2 (b INT);
INSERT INTO t2 VALUES (1),(2);

EXPLAIN SELECT * FROM t1 UNION SELECT * FROM t1
  ORDER BY (SELECT a FROM t2 WHERE b = 12);

EXPLAIN SELECT * FROM t2 UNION SELECT * FROM t2
  ORDER BY (SELECT * FROM t1 WHERE MATCH(a) AGAINST ('+abc' IN BOOLEAN MODE));

DROP TABLE t1,t2;

exit;