SQL Anti-Join Pattern

The formal name for 'rows in A with no match in B' — everything from the last two lessons, named properly.

What & Why

An anti-join returns rows from one table that have no corresponding match in another. It's not a distinct SQL keyword — it's the name for the pattern you get from NOT EXISTS or LEFT JOIN ... WHERE NULL.

See How It Works

BUSINESS QUESTION

Product wants features that have never received feedback.

id	name	description	team	released_at	deprecated_at
1	Activation Checklist	Guides new users through setup	growth	2024-01-20	NULL
2	CSV Export	Exports report data	platform	2024-02-14	NULL
3	Invite Nudges	Prompts workspace collaboration	growth	2024-03-05	NULL
4	Legacy Dashboard	Original reporting surface	analytics	2023-08-10	2024-06-01

id	user_id	feature_id	rating	nps_score	comment	created_at
1	101	1	5	9	Clear and useful	2024-01-25 12:15:00+00
2	102	2	4	NULL	Export worked well	2024-02-20 15:40:00+00
3	103	1	4	7	Helpful setup flow	2024-03-18 09:05:00+00
4	104	3	3	NULL	Needs clearer timing	2024-04-08 17:30:00+00

Watch NOT EXISTS keep the feature with no feedbackStep 1 of 4

NOT EXISTS product.feedback where feedback.feature_id = feature.id

feature_id	feature	feedback_ids	decision
1	Activation Checklist	1, 3	SKIP
2	CSV Export	2	SKIP
3	Invite Nudges	4	SKIP
4	Legacy Dashboard	—	KEEP

Activation Checklist has two feedback rows.

EXAMPLE QUERY

SELECT
  f.id AS feature_id,
  f.name
FROM product.features f
WHERE NOT EXISTS (
  SELECT 1
  FROM product.feedback fb
  WHERE fb.feature_id = f.id
)
ORDER BY feature_id;

This lesson's practice is part of Pro.

See what's included →

Advanced business practice