MySQL查询四张表的行数

-- 查询四张表的行数
SELECT a.countNum AS userId,b.countNum AS discussId,c.countNum AS flightId,d.countNum AS orderId,e.countNum AS adminId
FROM (
	(SELECT COUNT(*)as countNum FROM user) a,
	(SELECT COUNT(*)as countNum FROM discuss) b,
	(SELECT COUNT(*)as countNum FROM flight) c,
	(SELECT COUNT(*)as countNum FROM `order`) d,
	(SELECT COUNT(*)as countNum FROM admin) e
)