php mysql双表查询及三表查询

双表

SELECT A. * , B. * 
FROM memberdata A LEFT JOIN members B ON A.uid = B.uid
WHERE 1 
LIMIT 0 , 30

三表

SELECT * FROM tx1 left join (tx2, tx3) ON (tx1.id=tx2.tid AND tx2.tid=tx3.tid) where tx1.id = 3