SQL Subquery in WHERE
The most common home for a subquery — filtering rows using a value the query computes itself.
What & Why
A subquery inside WHERE computes something to filter against — a single number, or a whole list — before the outer query decides which rows survive.
See How It Works
BUSINESS QUESTION
Return campaigns whose spend is above the overall campaign average.
| 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 |
Watch a WHERE subquery calculate, compare, then filterStep 1 of 3
SELECT AVG(spend) FROM marketing.campaigns
| inner input rows | average spend |
|---|---|
| 4 campaigns | 52,500.00 |
The inner query resolves first and returns exactly one benchmark value.
EXAMPLE QUERY
SELECT
id AS campaign_id,
name,
spend
FROM marketing.campaigns
WHERE spend > (
SELECT AVG(spend)
FROM marketing.campaigns
)
ORDER BY spend DESC, campaign_id;This lesson's practice is part of Pro.
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