SQL Percentiles
The median generalized — any percentile, not just the 50th.
What & Why
PERCENTILE_CONT(p) works for any p between 0 and 1 — the median from the previous lesson was just the special case p = 0.5.
See How It Works
BUSINESS QUESTION
Marketing wants median and 90th-percentile campaign spend by channel.
| 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
channel,
ROUND(PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY spend)::numeric, 2) AS p50_spend,
ROUND(PERCENTILE_CONT(0.9) WITHIN GROUP (ORDER BY spend)::numeric, 2) AS p90_spend
FROM marketing.campaigns
GROUP BY channel
ORDER BY channel;RESULT — continuous spend percentiles
| channel | p50_spend | p90_spend |
|---|---|---|
| 45000.00 | 45000.00 | |
| google_ads | 57500.00 | 59500.00 |
| 50000.00 | 50000.00 |
The google_ads p90 interpolates between 55,000 and 60,000.
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