In SQL, click-through rate for the whole period is ROUND(100.0 * SUM(ad_clicks) / SUM(ad_impressions), 2) over the monthly table. On the sample data it returns 1.22.
CTR = Clicks ÷ Impressions × 100
What you need
Click-through rate (CTR) is the percentage of ad impressions that led to a click: clicks divided by impressions, times 100. You need these columns, here from the sample file monthly.csv:
- ad_impressions: ad impressions
- ad_clicks: ad clicks
CREATE TABLE monthly (
month TEXT, -- 'YYYY-MM'
ad_impressions INTEGER,
ad_clicks INTEGER
);Step by step
- Load monthly.csv into a table called monthly. The table only needs the month column and the columns below.
- Run the first query to get one row per month.
- Run the whole-period query. It adds up each column first and divides once; averaging the monthly results gives a different, usually wrong, answer.
The queries
SELECT
month,
ROUND(100.0 * ad_clicks / NULLIF(ad_impressions, 0), 2) AS ctr
FROM monthly
ORDER BY month;SELECT ROUND(100.0 * SUM(ad_clicks) / NULLIF(SUM(ad_impressions), 0), 2) AS ctr
FROM monthly;What you should get
Run against the sample data, the code above returns these values (in percent):
| Month | ad_impressions | ad_clicks | ctr |
|---|---|---|---|
| 2026-01 | 8,20,000 | 9,840 | 1.20% |
| 2026-02 | 8,65,000 | 10,380 | 1.20% |
| 2026-03 | 9,40,000 | 11,750 | 1.25% |
| 2026-04 | 8,80,000 | 10,120 | 1.15% |
| 2026-05 | 9,90,000 | 12,380 | 1.25% |
| 2026-06 | 10,50,000 | 13,340 | 1.27% |
| Whole period | 55,45,000 | 67,810 | 1.22% |
67,810 ÷ 55,45,000 × 100 = 1.22%
Notes for SQL
- Integer columns divide as integers in PostgreSQL, SQLite and SQL Server, so 3 / 4 gives 0. Multiplying by 1.0 (or 100.0) first makes the division decimal.
- NULLIF(x, 0) turns a zero denominator into NULL, so the query returns NULL for that row instead of failing with a division-by-zero error.
- Tested on SQLite and DuckDB. SUM, NULLIF and ROUND work the same in PostgreSQL, MySQL and BigQuery; SQL Server uses TOP instead of LIMIT where a query has one.
Where click-through rate misleads
- Accidental clicks on mobile placements inflate CTR. Check time on site for those clicks.
- CTR for search ads and for social ads are not comparable.
- Small campaigns give noisy rates. A difference of a few clicks is not a result.
The full explanation, with a calculator, is on the Click-through rate (CTR) page.
Same metric, other tools
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About the data on this page
The figures come from a small made-up dataset, printed above in full so you can check every number by hand. Download it as monthly.csv. The results are computed from those rows when the page is built, and the Excel formulas, SQL and Python on these pages are run against the same rows before publishing, so the code and the answers agree.
To get these numbers from your own data without writing formulas, try AnalyzeIt: ask in plain words and it shows the working behind every figure.
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