SQL Join for Payroll Updates | Dataford Interview Questions

Automatic Data Processing wants to identify employees whose payroll processing information is missing or stale. Write a SQL query to return employees whose most recent payroll update was more than 30 days before September 26, 2026, or who have no valid update date.

Output

Return one row per employee, including employees without matching payroll updates.
Include employee_id, employee_name, department, and last_update_at, where last_update_at is the employee's most recent non-null update date.
Include employees with no valid update date or with a last update before August 27, 2026. Employees updated on or after August 27, 2026 are excluded.
Treat null update dates as missing, and order the results by employee_id ascending.

Schema

employees

Column	Type	Description
employee_idPK	INT	Unique employee identifier
employee_name	VARCHAR(100)	Employee full name
department	VARCHAR(80)	Employee department

payroll_processing_updates

Column	Type	Description
update_idPK	INT	Unique payroll update identifier
employee_id	INT	Employee associated with the payroll update
updated_at	DATE	Date the payroll processing update was received
update_status	VARCHAR(30)	Status recorded for the payroll update

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Problem