Grokking the Data Engineering Interview
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Slowly Changing Dimensions

A bakery chain's finance team runs one query at the end of each reporting period: sales per region for days 1 to 40. On day 40 it returned these totals:

SELECT st.region, SUM(s.sales_cents) AS sales_cents
FROM daily_sales s
JOIN stores st ON st.store_code = s.store_code
WHERE s.day_no BETWEEN 1 AND 40
GROUP BY st.region
ORDER BY st.region;

Output:

+--------+-------------+
| region | sales_cents |
+--------+-------------+
| East   |       58000 |
| North  |      138000 |
+--------+-------------+

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