join&Union

原文链接： http://www.cnblogs.com/enhance/p/10980459.html

id	name	id	name
1	zhangsan	1	hanmeimei
2	lisi	2	wangwu
3	wangwu

join:select * from A join B on A.name=B.name -----取交集

id	name	id	name
1	wangwu	2	wangwu

full/out join:select * from A full join B on A.name=B.name  ----取并集

id	name	id	name
1	zhangsan	null	null
2	lisi	null	null
3	wangwu	2	wangwu
null	null	1	hanmeimei

left join:select * from A left join B on A.name=B.name

id	name	id	name
1	zhangsan	null	null
2	lisi	null	null
3	wangwu	2	wangwu

right join: select * from A right join B on B.name

id	name	id	name
null	null	1	hanmeimei
3	wangwu	2	wangwu

union:select name from A union select name from B(union和union all中的select语句需要相同的查询列)

name

zhangsan

lisi

wangwu

hanmeimei

union all：较union区别是union会将重复值合并，而union all不会合并

　　　　select name from A union all select name from B

name

zhangsan lisi wangwu hanmeimei

wangwu

转载于:https://www.cnblogs.com/enhance/p/10980459.html