Code reviewHardcr-g649

Subject Sql index designLevel Senior–Staff~26 minCommon in Databases & SQL interviewsIndustries Software development

Question

Review this query and the index that was added to 'fix' it.

The `messages` table has 500M rows across ~100k channels.

What a strong answer looks like

Separate real bugs from style. Rank issues by severity, point at the root cause rather than the symptom, and suggest a concrete fix — specific and kind.

Learn the concepts

Talk through your review

Code to reviewsql

1-- hot query2SELECT id, body3FROM messages4WHERE channel_id = 425  AND created_at >= now() - interval '7 days'6ORDER BY created_at DESC7LIMIT 50;8 9-- the index someone added10CREATE INDEX idx_messages_created ON messages (created_at);

Run or narrate your approach, then ask the coach.