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;

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