1378.
展示每位用户的 唯一标识码（unique ID ）；如果某位员工没有唯一标识码，使用 null 填充即可。 你可以以任意顺序返回结果表。
题目链接：
https://leetcode.cn/problems/replace-employee-id-with-the-unique-identifier/
建表插入数据：
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')画图分析：
代码实现：
select e.unique_id,name
from employees s left join employeeuni e
on s.id=e.id ;
