SQL Variance
Standard deviation, before the square root — the same spread, in squared units.
What & Why
Variance is standard deviation squared. It's the same underlying calculation — STDDEV just takes the square root at the end to bring the units back to something directly comparable to the original data (dollars, not dollars-squared).
See How It Works
BUSINESS QUESTION
Compare campaign-spend variance across channels.
| 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,
COUNT(*) AS campaigns,
ROUND(VAR_SAMP(spend), 2) AS sample_variance_spend
FROM marketing.campaigns
GROUP BY channel
ORDER BY sample_variance_spend DESC NULLS LAST, channel;RESULT — sample spend variance
| channel | campaigns | sample_variance_spend |
|---|---|---|
| google_ads | 2 | 12500000.00 |
| 1 | NULL | |
| 1 | NULL |
Only the two-row google_ads group has a defined sample variance.
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