mysql中join的七种用法

mysql中join的七种用法

内连接
inner join：

SELECT * FROM hotel h INNER JOIN room r ON h.id = r.hotelid

左外连接
left join：

SELECT * FROM hotel h LEFT  OUTER JOIN room r ON h.id = r.hotelid

右外连接
right join：

SELECT * FROM hotel h RIGHT OUTER JOIN room r ON h.id = r.hotelid

左连接

SELECT * FROM hotel h LEFT  JOIN room r ON h.id = r.hotelid WHERE r.hotelid IS NULL

右连接

SELECT * FROM hotel h RIGHT JOIN room r ON h.id = r.hotelid WHERE r.hotelid IS NULL

全连接

SELECT * FROM hotel h RIGHT JOIN room r ON h.id = r.hotelid UNION
SELECT * FROM hotel h LEFT  JOIN room r ON h.id = r.hotelid

两张表中均没有出现的数据集

SELECT * FROM hotel h RIGHT JOIN room r ON h.id = r.hotelid WHERE h.id IS NULL
UNION SELECT * FROM hotel h LEFT  JOIN room r ON h.id = r.hotelid WHERE r.hotelid IS NULL