CREATE TABLE t1(a INT) ENGINE=InnoDB;

INSERT INTO t1 VALUES (0);

SELECT DISTINCT POW(COUNT(*), @a:=(SELECT 1 FROM t1 LEFT JOIN t1 AS t2 ON @a))

AS b FROM t1 GROUP BY a;

SELECT @a;

DROP TABLE t1;

CREATE TABLE t1(f1 INT, f2 INT);

INSERT INTO t1 VALUES (1,2),(2,3),(3,1);

CREATE TABLE t2(a INT);

INSERT INTO t2 VALUES (1);

SET @var=NULL;

SELECT @var:=(SELECT f2 FROM t2 WHERE @var) FROM t1 GROUP BY f1 ORDER BY f2 DESC

LIMIT 1;

SELECT @var;

DROP TABLE t1, t2;