Solved -> 1978. Employees Whose Manager Left the Company

Author: NandiSoham

06_Subqueries/1978. Employees Whose Manager Left the Company.sql

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+/*
+
+Problem Link -> https://leetcode.com/problems/employees-whose-manager-left-the-company/description/?envType=study-plan-v2&envId=top-sql-50
+
+------------------------------------------------------------- QUESTION -----------------------------------------------------------
+
+Table: Employees
+
++-------------+----------+
+| Column Name | Type     |
++-------------+----------+
+| employee_id | int      |
+| name        | varchar  |
+| manager_id  | int      |
+| salary      | int      |
++-------------+----------+
+In SQL, 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). 
+ 
+
+Find 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 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.
+
+*/
+
+-- ----------------------------------------------------------- SOLUTION -----------------------------------------------------------
+
+SELECT employee_id
+FROM Employees
+WHERE salary < 30000
+AND manager_id NOT IN (
+    SELECT employee_id
+    FROM Employees
+)
+ORDER BY employee_id
+