SQL Non-Correlated Subquery
Runs once, independently — the far more common case, and the opposite of correlated.
What & Why
A non-correlated subquery doesn't reference anything from the outer query — it's a complete, independent question that runs exactly once, and every outer row compares against that same single answer.
Nearly every subquery in this series so far has been non-correlated. The correlated subquery lesson is the exception, not the rule.
See How It Works
BUSINESS QUESTION
Marketing wants campaigns above one global spend benchmark.
| id | name | channel | spend | start_date | end_date | status | target_segment |
|---|---|---|---|---|---|---|---|
| 1 | Spring Launch | google_ads | 55000.00 | 2024-01-15 | 2024-03-31 | active | smb |
| 2 | Retention Webinar | 45000.00 | 2024-02-10 | 2024-04-15 | active | enterprise | |
| 3 | Finance Retargeting | 50000.00 | 2024-03-12 | 2024-05-31 | active | enterprise | |
| 4 | Enterprise Search | google_ads | 60000.00 | 2024-04-01 | 2024-06-30 | active | enterprise |
EXAMPLE QUERY
SELECT
id AS campaign_id,
name,
spend
FROM marketing.campaigns
WHERE spend > (SELECT PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY spend) FROM marketing.campaigns)
ORDER BY spend DESC, campaign_id;RESULT — spend above the 52,500 median
| campaign_id | name | spend |
|---|---|---|
| 4 | Enterprise Search | 60000.00 |
| 1 | Spring Launch | 55000.00 |
The independent subquery calculates the campaign-spend median once.
This lesson's practice is part of Pro.
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