Explain Query Performance Trade-offs | Dataford Interview Questions

Explain query performance trade-offs in a production environment.

Using the provided schema, write a PostgreSQL query that returns eligible accounts and their completed verification counts during 2025. The result should preserve accounts with no matching checks.

Output

One row per account created before 2025-01-01
Columns: account_id, account_name, completed_checks
Include only checks completed during 2025
Order by completed_checks descending, then account_id ascending

Schema

accounts

Column	Type	Description
account_idPK	INT	Unique account identifier
account_name	VARCHAR(120)	Display name of the account
created_at	TIMESTAMP	Account creation timestamp

verification_checks

Column	Type	Description
check_idPK	INT	Unique verification check identifier
account_id	INT	Account associated with the check
status	VARCHAR(20)	Check outcome status
checked_at	TIMESTAMP	Time the verification check was performed

Your question is Explain Query Performance Trade-offs. 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