Description
Write a SQL query to find employees who work in departments with only one employee. Return employee_id.
Table:
employees| Column | Type |
|---|---|
| employee_id | INT |
| department_id | INT |
Examples
Input:
CREATE TABLE employees (employee_id INT, department_id INT); INSERT INTO employees VALUES (1, 1), (2, 1), (3, 2);Output:
3Explanation:
Employees 1 and 2 are both in department 1, so neither qualifies. Employee 3 is alone in department 2, so they are returned.
Input:
CREATE TABLE employees (employee_id INT, department_id INT); INSERT INTO employees VALUES (101, 10), (102, 20), (103, 20), (104, 30), (105, 30), (106, 40);Output:
101, 106Explanation:
Employee 101 is the only one in department 10, and employee 106 is the only one in department 40. Departments 20 and 30 each have 2 employees, so those employees are excluded.
Input:
CREATE TABLE employees (employee_id INT, department_id INT); INSERT INTO employees VALUES (5, 100), (6, 200), (7, 200), (8, 200), (9, 300), (10, 400), (11, 400);Output:
5, 9Explanation:
Employee 5 is alone in department 100 and employee 9 is alone in department 300. Department 200 has 3 employees and department 400 has 2 employees, so those don't qualify as unique departments.
Constraints
- •
Use GROUP BY with HAVING COUNT = 1