Optimize SQL Query Performance | Dataford Interview Questions

What steps would you take to ensure that your SQL queries are optimized for performance?

Using the provided PostgreSQL schema, write the query that should be optimized and describe the checks, indexing decisions, and validation steps you would use. The result must include active employees and their payroll totals for the first quarter of 2025.

Output

One row per active employee, including employees without qualifying payroll records.
Columns: employee_id, employee_name, total_paid, payment_count.
Sort by total_paid descending, then employee_id ascending.

Schema

employees

Column	Type	Description
employee_idPK	INT	Unique employee identifier
employee_name	VARCHAR(100)	Employee display name
status	VARCHAR(20)	Employment status

payroll_records

Column	Type	Description
payroll_idPK	INT	Unique payroll record identifier
employee_id	INT	Employee associated with the payroll record
paid_at	TIMESTAMP	Timestamp when the payroll payment was issued
amount	NUMERIC(12,2)	Payment amount

Your question is Optimize SQL Query Performance. Start with the requirements and the two tables in the Question tab.

Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.

Problem