SQl中的左连接，右连接，内连接，全连接，自连接的理解。

    按照自己的理解做个笔记，以下在Sql Server2005和Oracle92中都运行通过：

create table a(
   aid varchar(2),
   aname varchar(10),
   bid varchar(2) );

create table b(
   bid varchar(2),
   bname varchar(10));

insert into a values(‘s1′,’sname1′,’c1’);
insert into a values(‘s2′,’sname2′,’c2’);
insert into a values(‘s3′,’sname3′,’c3’);
insert into a values(‘s4′,’sname4′,’c4’);
insert into a values(‘s5′,’sname5′,’c5’);

insert into b values(‘c1′,’cname1’);
insert into b values(‘c2′,’cname2’);
insert into b values(‘c3′,’cname3’);
insert into b values(‘c6′,’cname6’);
insert into b values(‘c7′,’cname7’);

–Iner Join和Join和, (如select * from a,b where a.id=b.id)，这三个效果一样.

select * from  a ,  b where  a.bid = b.bid;
select * from a join b on a.bid = b.bid;
select * from a inner join b on a.bid = b.bid;

–Left Join和Left Outer Join 左连接、左外连接，效果一样。
select * from a left join b on a.bid = b.bid;
select * from a left outer join b on a.bid = b.bid;

–Right Join和Right Outer Join 右连接、右外连接，效果一样。

select * from a right join b on a.bid = b.bid;
select * from a right outer join b on a.bid = b.bid;

–Full Join和Full Outer Join 全连接、全外连接，效果一样。

select * from a full join b on a.bid = b.bid;
select * from  a full outer join  b on a.bid = b.bid;

–Cross Join，不带where，即笛卡尔积。

select * from a  Cross join b;

总结：只有以上的的连接词，像什么Left Inner Join、Right Full Join之类的组合都没有，想都别想！！