1. 内连接很简单 select A.*, B.* from A,B where A.id = B.id select A.*, B.* from A inner join B on A.id = B.id2. 左外连接 select * from emp a left join dept d on a.deptno=d.deptno select * from emp a,dept d where a.deptno=d.deptno(+) 3. 右外连接 select * from emp a right join dept d on a.deptno=d.deptno select * from emp a,dept d where a.deptno(+)=d.deptno
例:select t1.*,t2.* from a表,b表 where a.id(+)=b.id
(+)号在左边表示查询出来的记录数以右边表(即 b表)的记录数为准
http://blog.csdn.net/cchaha/archive/2009/09/08/4530838.aspx
select A.*, B.* from A,B where A.id = B.id
select A.*, B.* from A inner join B on A.id = B.id2. 左外连接
select * from emp a left join dept d on a.deptno=d.deptno
select * from emp a,dept d where a.deptno=d.deptno(+)
3. 右外连接
select * from emp a right join dept d on a.deptno=d.deptno
select * from emp a,dept d where a.deptno(+)=d.deptno
(+)连接符放在想查询的行中包含空值的列(列1)相反的一边 (列2)
左连接和右连接+写左边为右连接,相当于right join+写右边为左连接,相当于left join