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by mulmen 804 days ago
I’ll stop short of calling comparisons to standard SQL disingenuous but it’s definitely unrealistic because no standard SQL implementation exists.

What does this “last” operation do? There’s definitely a LAST_VALUE() window function in the databases I use. It is available in Postgres, Redshift, EMR, Oracle, MySQL, MSSQL, Bigquery, and certainly others I am not aware of.
1 comments
better365 803 days ago
That's fair.

Actually, Last is usually called last_k(n), so that you can specify the number of the values in the result array. For example, if the input column is page_view_id and n = 300, it will return the last 300 page_view_id as an array. If a window is used, for example, 7d, it will truncate the results to the past 7d. The LAST_VALUE() seems to return the last value from an ordered set. Hope that helps. Thanks for your interests.

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mulmen 803 days ago
In SQL we do that with a RANK window function then apply a filter to that rank. It can also be done with a correlated subquery.
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