Primary Department for Each Employee

Task: Report all the employees with their primary department. For employees who belong to one department, report their only department.

Table: Employee

+---------------+------------+
| Column Name   | Type       |
+---------------+------------+
| employee_id   | INT        |
| department_id | INT        |
| primary_flag  | varchar(1) |
+---------------+------------+

Input: Employee table:

+-------------+---------------+--------------+
| employee_id | department_id | primary_flag |
+-------------+---------------+--------------+
| 1           | 1             | N            |
| 2           | 1             | Y            |
| 2           | 2             | N            |
| 3           | 3             | N            |
| 4           | 2             | N            |
| 4           | 3             | Y            |
| 4           | 4             | N            |
+-------------+---------------+--------------+

Output:

+-------------+---------------+
| employee_id | department_id |
+-------------+---------------+
| 1           | 1             |
| 2           | 1             |
| 3           | 3             |
| 4           | 3             |
+-------------+---------------+