1965 Employees With Missing Information.md

1965. Employees With Missing Information

https://leetcode.cn/problems/employees-with-missing-information/
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.

solution

# Write your MySQL query statement below
SELECT 
    e.employee_id
FROM Employees e
LEFT JOIN Salaries s USING(employee_id)
WHERE s.salary IS NULL
UNION
SELECT 
    s.employee_id
FROM Salaries s
LEFT JOIN Employees e USING(employee_id)
WHERE e.name IS NULL
ORDER BY employee_id