How do window functions and the group by clause interact?

Question

I do understand window functions and group by separately.

But what happens when you use both a window function and a group by clause in the same query ?

Are the selected rows grouped first, then considered by the window function ?
Or does the window function executes first, then the resulting values are grouped by group by ?
Something else ?

score 15 · Accepted Answer · answered May 18 '16 at 08:42

15

If the query contains any window functions, these functions are evaluated after any grouping, aggregation, and HAVING filtering is performed

^{emphasis mine}

answered May 18 '16 at 08:42

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