[1965_EASY] Employees With Missing Information

Employees With Missing Information - LeetCode

Table: Employees

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| employee_id | int     |
| name        | varchar |
+-------------+---------+
employee_id is the primary key for this table.
Each row of this table indicates the name of the employee whose ID is employee_id.

 

Table: Salaries

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| employee_id | int     |
| salary      | int     |
+-------------+---------+
employee_id is the primary key for this table.
Each row of this table indicates the salary of the employee whose ID is employee_id.

 

Write an SQL query to report the IDs of all the employees with missing information. The information of an employee is missing if:

• The employee's name is missing, or
• The employee's salary is missing.

Return the result table ordered by employee_id in ascending order.

The query result format is in the following example.

 

Example 1:

Input: 
Employees table:
+-------------+----------+
| employee_id | name     |
+-------------+----------+
| 2           | Crew     |
| 4           | Haven    |
| 5           | Kristian |
+-------------+----------+
Salaries table:
+-------------+--------+
| employee_id | salary |
+-------------+--------+
| 5           | 76071  |
| 1           | 22517  |
| 4           | 63539  |
+-------------+--------+
Output: 
+-------------+
| employee_id |
+-------------+
| 1           |
| 2           |
+-------------+
Explanation: 
Employees 1, 2, 4, and 5 are working at this company.
The name of employee 1 is missing.
The salary of employee 2 is missing.

 

문제 조건

- 직원의 이름 누락 혹은 급여가 누락된 직원의 ID를 출력하시오 

- employee_id를 기준으로 오름차순 하시오 

 

문제 풀이 

- name이 누락된 테이블, salary가 누락 된 테이블을 생성

   - left join을 이용해서 employees와 salary 테이블을 연결시키고 각 null값이 있는 employee_id를 출력

- 그 다음 누락된 정보가 담긴 두 테이블을 union으로 합쳐줌 

select e.employee_id 
from employees e 
    left join salaries s on e.employee_id = s.employee_id
where s.salary is null

union

select s.employee_id
from salaries s 
    left join employees e on s.employee_id = e.employee_id
where e.name is null 
order by 1