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Formatted question description: https://leetcode.ca/all/1965.html
1965. Employees With Missing Information
Level
Easy
Description
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:
Employees table:
+-------------+----------+
| employee_id | name |
+-------------+----------+
| 2 | Crew |
| 4 | Haven |
| 5 | Kristian |
+-------------+----------+
Salaries table:
+-------------+--------+
| employee_id | salary |
+-------------+--------+
| 5 | 76071 |
| 1 | 22517 |
| 4 | 63539 |
+-------------+--------+
Result table:
+-------------+
| employee_id |
+-------------+
| 1 |
| 2 |
+-------------+
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
Join the two tables using employee_id. Keep the entries that have one field null.
# Write your MySQL query statement below
select e.employee_id
from Employees e
left join Salaries s
using(employee_id)
where salary is null
union all
select s.employee_id
from Employees e
right join Salaries s
using(employee_id)
where name is null
order by employee_id;