Optimize Slow Client Query

How would you optimize a database query that is performing slowly for a client with millions of records?

Using the provided PostgreSQL schema, return the latest completed attempt for each active candidate and active assessment since 2025-01-01. Include prior score information and recorded event metrics so the query can be evaluated for correctness and performance.

Output

1. One row per candidate and assessment combination with a qualifying completed attempt.
2. Columns: candidate_name, assessment_name, completed_at, score, previous_score, score_change, event_count, and total_duration_seconds.
3. Include candidates with no matching events, treating their event count and duration as zero.
4. Sort by completed_at descending, then candidate_name, then assessment_name.