Employees Whose Manager Left the Company - Leetcode 1978 | Week 4 | Qs 18 | SQL

Leetcode - 1978. Employees Whose Manager Left the Company
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SQL Question
Write an SQL query to report the IDs of the employees whose salary is strictly less than $30000 and whose manager left the company.
SQL Schema
Create table If Not Exists Employees (employee_id int, name varchar(20), manager_id int, salary int)
Truncate table Employees
insert into Employees (employee_id, name, manager_id, salary) values ('3', 'Mila', '9', '60301')
insert into Employees (employee_id, name, manager_id, salary) values ('12', 'Antonella', 'None', '31000')
insert into Employees (employee_id, name, manager_id, salary) values ('13', 'Emery', 'None', '67084')
insert into Employees (employee_id, name, manager_id, salary) values ('1', 'Kalel', '11', '21241')
insert into Employees (employee_id, name, manager_id, salary) values ('9', 'Mikaela', 'None', '50937')
insert into Employees (employee_id, name, manager_id, salary) values ('11', 'Joziah', '6', '28485')
Table: Employees
+-----------------------+--------------+
| Column Name | Type |
+-----------------------+--------------+
| employee_id | int |
| name | varchar |
| manager_id | int |
| salary | int |
+----------------------+--------------+
employee_id is the primary key for this table.
This table contains information about the employees, their salary, and the ID of their manager. Some employees do not have a manager (manager_id is null).
Write an SQL query to report the IDs of the employees whose salary is strictly less than $30000 and whose manager left the company. When a manager leaves the company, their information is deleted from the Employees table, but the reports still have their manager_id set to the manager that left.
Return the result table ordered by employee_id.
The query result format is in the following example.
Example 1:
Input:
Employees table:
+--------------------+-------------------+-------------------+----------+
| employee_id | name | manager_id | salary |
+--------------------+-------------------+--------------------+----------+
| 3 | Mila | 9 | 60301 |
| 12 | Antonella | null | 31000 |
| 13 | Emery | null | 67084 |
| 1 | Kalel | 11 | 21241 |
| 9 | Mikaela | null | 50937 |
| 11 | Joziah | 6 | 28485 |
+-------------------+-----------------+----------------------+--------+
Output:
+-------------+
| employee_id |
+-------------+
| 11 |
+-------------+
Explanation:
The employees with a salary less than $30000 are 1 (Kalel) and 11 (Joziah).
Kalel's manager is employee 11, who is still in the company (Joziah).
Joziah's manager is employee 6, who left the company because there is no row for employee 6 as it was deleted