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Comment by dan-robertson | Hacker News Reader

I’m not sure the sub query would be necessary if the weird ast-based naming didn’t exist. Couldn’t you just write:

  SELECT a+1 AS a1 FROM t GROUP BY a1

?

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You can do that in PostgreSQL, but not according to the spec, apparently, and the PostgreSQL developers regret the feature. [0] (As someone who's spent a lot of time trying to simulate PostgreSQL's name resolution rules... it's reassuring to know that the rules are painful inside of PostgreSQL too.)

[0]: https://www.postgresql.org/message-id/7608.1259177709%40sss....

I never figured out why AS isn't allowed in the GROUP BY clause. It would be much simpler to implement `SELECT a1 FROM nums GROUP BY a+1 AS a1`.

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