[MySQL] LEFT JOIN

이거슨 leet code의 1378 문제

 

 

- SQL Schema

Create table If Not Exists Employees (id int, name varchar(20))
Create table If Not Exists EmployeeUNI (id int, unique_id int)
Truncate table Employees
insert into Employees (id, name) values ('1', 'Alice')
insert into Employees (id, name) values ('7', 'Bob')
insert into Employees (id, name) values ('11', 'Meir')
insert into Employees (id, name) values ('90', 'Winston')
insert into Employees (id, name) values ('3', 'Jonathan')
Truncate table EmployeeUNI
insert into EmployeeUNI (id, unique_id) values ('3', '1')
insert into EmployeeUNI (id, unique_id) values ('11', '2')
insert into EmployeeUNI (id, unique_id) values ('90', '3')

 

join 하고 unique_id, name을 출력한다.

만약 unique_id가 없다면 null로 표기한다.

 

 

- solution

SELECT unique_id, name
FROM Employees as emp
LEFT JOIN EmployeeUNI as uni
ON uni.id = emp.id