A Short Story About SQL’s Biggest Rival

Re:A Short Story About SQL’s Biggest Rival by wenc on Friday October 09, 2020 @05:32PM (#24734669)

I consider myself a fan of SQL, but my nitpick is more around named calculated columns. For instance:

    SELECT AVG(col1) OVER (PARTITION BY col2) AS partcol1
    FROM tbl
    WHERE AVG(col1) OVER (PARTITION BY col2) > 10.0

I wish I could just do:

    SELECT AVG(col1) OVER (PARTITION BY col2) AS partcol1
    FROM tbl
    WHERE partcol1 > 10.0

But I can't, because the WHERE clause is processed before the SELECT clause.

So if I have a bunch of these and want a convenient way to work with the named columns, I have to wrap them into a common table expression:

    WITH cte AS (
        SELECT AVG(col1) OVER (PARTITION BY col2) AS partcol1
        FROM tbl
    )
    SELECT partcol1
    FROM cte
    WHERE partcol1 > 10.0

So wordy.

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Re:A Short Story About SQL’s Biggest Rival by SPBS on Saturday October 10, 2020 @12:08AM (#24736627)

Yeah it's mentioned in this blog post https://blog.jooq.org/2014/01/06/the-sql-languages-most-miss... that SQL is missing Common Column Expressions, and that using Common Table Expressions reuse columns is simply a band-aid fix over the lack of those.

For example, your example would have been more naturally expressed as

    SELECT partcol1
    FROM (tbl WITH partcol1 AS AVG(col1) OVER (PARTITION BY col2))
    WHERE partcol1 > 10.0

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Re:A Short Story About SQL’s Biggest Rival by wenc on Saturday October 10, 2020 @12:49AM (#24736760)

Wow thanks. I've never heard it expressed as a Common Column Expression. It makes sense to include it in the FROM statement because that's usually parsed and executed first.

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