內外連接，顯隱式連接詳解

 

--建立一個user信息表

create table user_info(

id number(2) primary key,

name varchar2(10) unique

);

--插入數據

insert into user_info(id,name)values(1,'曹操');

insert into user_info(id,name)values(2,'劉備');

insert into user_info(id,name)values(3,'周瑜');

insert into user_info(id,name)values(4,'關羽');

insert into user_info(id,name)values(5,'張飛');

insert into user_info(id,name)values(6,'趙雲');

 

select * from user_info;

--建立地址表

create table address(

id number(2) primary key,

user_id number(2),

info varchar2(16)

);

--添加數據

insert into address(id,user_id,info)values(1,1,'河北唐山');

insert into address(id,user_id,info)values(2,2,'北京海淀');

insert into address(id,user_id,info)values(3,1,'河北邯鄲');

insert into address(id,user_id,info)values(4,2,'河北保定');

insert into address(id,user_id,info)values(5,3,'河南鄭州');

insert into address(id,user_id,info)values(6,5,'山西太原');

insert into address(id,user_id,info)values(7,4,'安徽合肥');

insert into address(id,user_id,info)values(8,2,'山東青島');

insert into address(id,user_id,info)values(9,9,'山東青島');

select * from address;

 

commit;

 

--隱式左/右外連接，outer能夠不寫

select u.*,a.* from user_info u left join address a on u.id=a.user_id;

select u.*,a.* from user_info u right join address a on u.id=a.user_id order by a.id;

--顯式左/右外連接

select u.*,a.* from user_info u left outer join address a on u.id = a.user_id;

select u.*,a.* from user_info u right outer join address a on u.id = a.user_id;

 

 

--隱式內鏈接，inner能夠省略，將on改成where

select u.*,a.* from user_info u,address a where u.id=a.user_id;

--顯式內鏈接,不分左右，不帶left或right，只顯示重合的數據，也就是取交集

select u.*,a.* from user_info u inner join address a on u.id=a.user_id;

 

 

--外連接的其餘寫法，+號和完整表位置相反

select u.*,a.* from user_info u,address a where u.id=a.user_id(+);--左外連接，+號在=號右面

select u.*,a.* from user_info u,address a where u.id(+)=a.user_id;--右外連接，+號在=號左面

 

--全鏈接,顯示兩個表中全部信息

select u.*,a.* from user_info u full join address a on u.id = a.user_id;

--交叉鏈接，取笛卡爾積

select u.*,a.* from user_info u cross join address a;

select u.*,a.* from user_info u, address a;