From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
---|---|
To: | Luca Ferrari <fluca1978(at)gmail(dot)com> |
Cc: | pgsql-general <pgsql-general(at)lists(dot)postgresql(dot)org> |
Subject: | Re: order by <tablename> |
Date: | 2021-06-10 13:32:16 |
Message-ID: | 1557628.1623331936@sss.pgh.pa.us |
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Lists: | pgsql-general |
Luca Ferrari <fluca1978(at)gmail(dot)com> writes:
> The ORDER BY rejects non existent columns (right) but accepts the
> table itself as an ordering expression.
As others have noted, this is basically taking the table name as a
whole-row variable, and then sorting per the rules for composite
types. I write to point out that you can often get some insight into
what the parser thought it was doing by examining the reverse-listing
for the query. The simplest way to do that is to create a view and
examine the view:
regression=# create view v as
regression-# select * from t order by t;
CREATE VIEW
regression=# \d+ v
View "public.v"
Column | Type | Collation | Nullable | Default | Storage | Description
--------+---------+-----------+----------+---------+---------+-------------
v | integer | | | | plain |
View definition:
SELECT t.v
FROM t
ORDER BY t.*;
The form "t.*" is a more explicit way to write a whole-row variable.
(IIRC, accepting it without "*" is a PostQUEL-ism that we've never
got rid of. I think that with "*", there's at least some support
for the concept in the SQL standard. But I'm insufficiently
caffeinated to want to go digging for that.)
regards, tom lane
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