Julia Evans jvns.ca

SQL queries don't start with SELECT  ↦

Yesterday I was working on an explanation of window functions, and I found myself googling “can you filter based on the result of a window function”. As in – can you filter the result of a window function in a WHERE or HAVING or something?

Eventually I concluded “window functions must run after WHERE and GROUP BY happen, so you can’t do it”. But this led me to a bigger question – what order do SQL queries actually run in?

Kind of a snappy headline because Julia is talking about order in terms of execution and most of the time we’re thinking about order in terms of authoring. But still, TIL!


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