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3.Join(麻蛋 废话不多说 有图有真相)
测试数据脚本
1 CREATE TABLE Atable 2 ( 3 S# INT, 4 Sname nvarchar(32), 5 Sage INT, 6 Sfrom nvarchar(8) 7 ) 8 9 10 insert into Atable 11 select 1,N‘刘一‘,18,N‘A‘ union all 12 select 2,N‘钱二‘,19,N‘A‘ union all 13 select 3,N‘张三‘,17,N‘A‘ union all 14 select 4,N‘李四‘,18,N‘A‘ 15 16 17 18 19 CREATE TABLE Btable 20 ( 21 S# INT, 22 Sname nvarchar(32), 23 Sage INT, 24 Sfrom nvarchar(8) 25 ) 26 27 28 insert into Btable 29 select 1,N‘李四‘,18,N‘B‘ union all 30 select 2,N‘tom‘,19, N‘B‘ union all 31 select 3,N‘刘一‘,17,N‘B‘ union all 32 select 4,N‘jack‘,18,N‘B‘
数据表
1)cross join：交叉连接不需要任何连接条件。两个表的的数据直接进行笛卡尔积运算。
SELECT * FROM Atable as A cross join Btable as B order by A.S#
2)inner join == join 内连接的功能是，把两个表相关联的记录列出来，必须是相关联的记录。
SELECT * FROM Atable as A INNER JOIN Btable as B ON A.Sname = B.Sname
3)left outer join == left join 产生表B的完全集，而A表中匹配的则有值，没有匹配的则以null值取代。
SELECT * FROM Atable as A left outer join Btable as B ON A.Sname = B.Sname
4)right outer join == right jion 产生表A的完全集，而B表中匹配的则有值，没有匹配的则以null值取代。
SELECT * FROM Atable as A right outer join Btable as B ON A.Sname = B.Sname
5)full outer join == full join 产生A和B的并集。但是需要注意的是，对于没有匹配的记录，则会以null做为值。
SELECT * FROM Atable as A full join Btable as B ON A.Sname = B.Sname
6)union与union all 区别就是联合查询的时候union会去重，union all不会去重
SELECT Sname FROM Atable UNION SELECT Sname FROM Btable SELECT Sname FROM Atable UNION ALL SELECT Sname FROM Btable
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原文地址：http://www.cnblogs.com/cnki/p/5264273.html
