QuerydrillMonth over month
An SQL exercise from Querydrill. Solve it with a SQL editor in your browser, checked on the rows it returns and again on changed data, and it is checked the moment you submit.
The task
Return each month (like 2025-01), its paid revenue, and the change from the previous month's paid revenue. The first month shows NULL for the change.
What this exercise teaches
Aggregate first, then use a window function on the aggregated rows.
A hint if you get stuck
Build monthly totals in a CTE, then apply LAG over the months.
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