create table Employees (
last_name varchar2(10),
department_id varchar2(10)
);
create table Department(
department_id varchar2(10),
department_name varchar2(10)
);
insert into Employees values ('tom','1');
insert into Employees values ('peter','2');
insert into Employees values ('alice','3');
insert into Employees values ('jenny','5');
insert into Employees values ('linda','7');
commit;
insert into Department values ('1','baidu');
insert into Department values ('2','tensun');
insert into Department values ('3','BTC');
insert into Department values ('4','EOS');
insert into Department values ('5','HSR');
insert into Department values ('6','OMG');
insert into Department values ('7','ETH');
commit;
select * from Employees;
select * from Department ;
/*
左连接验证(左边一共5条数据，查出来大于左边的5条，怎么解释，)
*/
select e.last_name, e.department_id, d.department_name
from Employees e
left outer join Department d on e.department_id = d.department_id;
LAST_NAME DEPARTMENT_ID
1 tom 1
2 peter 2
3 alice 3
4 jenny 5
5 linda 7
DEPARTMENT_ID DEPARTMENT_NAME
1 1 baidu
2 2 tensun
3 3 BTC
4 4 EOS
5 5 HSR
6 6 OMG
7 1 woniupp
LAST_NAME DEPARTMENT_ID DEPARTMENT_NAME
1 1 baidu
2 peter 2 tensun
3 alice 3 BTC
4 jenny 5 HSR
5 tom 1 woniupp
6 linda 7
