Return Every Row in a Normalized Duplicate Group

Exercise brief

Understand the request

Data remediation analyst The review queue needs row-level evidence for every normalized email collision, not just one aggregate per email.

The review queue needs row-level evidence for every normalized email collision, not just one aggregate per email. Use a correlated EXISTS check to return every record with another record sharing its normalized email.

Data you will use

Review the relevant tables before deciding how to join, filter, or aggregate them.

Hints, when you need them

Open one clue at a time so you still do the reasoning.

Verified SQL answer

Attempt the problem first, then compare structure and reasoning—not just syntax.

SELECT q.record_id, q.customer_key, q.email, LOWER(TRIM(q.email)) AS normalized_email FROM quality_records q WHERE q.email IS NOT NULL AND TRIM(q.email) <> '' AND EXISTS (SELECT 1 FROM quality_records other WHERE other.record_id <> q.record_id AND other.email IS NOT NULL AND TRIM(other.email) <> '' AND LOWER(TRIM(other.email)) = LOWER(TRIM(q.email))) ORDER BY normalized_email, q.record_id;

Expected result

Use this output to verify values, aliases, ordering, and row count.