SQL interview question: Replace NULL With COALESCE
Handle Missing Data with COALESCE
The org chart page breaks on employees with no manager: their manager_id is NULL. The frontend team needs a safe fallback.
Use COALESCE to show 'none' wherever manager_id is NULL.
Return first_name, last_name, and reports_to (the COALESCE result). Order by last_name.
Skills: COALESCE for NULL handling
Tables
employees 37 rows
- id integer PK
- first_name text
- last_name text
- email text
- department_id integer → departments
- salary integer
- hire_date text
- manager_id integer → employees
- title text
| id | first_name | last_name | department_id | salary | hire_date | manager_id | title | |
|---|---|---|---|---|---|---|---|---|
| 1 | Alice | Chen | [email protected] | 1 | 250000 | 2015-01-15 | NULL | CEO |
| 2 | Robert | Martinez | [email protected] | 2 | 180000 | 2016-03-20 | NULL | CEO |
| 3 | Sarah | Johnson | [email protected] | 1 | 150000 | 2017-06-10 | 1 | VP Engineering |