Обсуждение: BUG #17232: DISTINCT ON does not allow AS

The following bug has been logged on the website:

Bug reference:      17232
Logged by:          Kyle Lahnakoski
Email address:      kyle@lahnakoski.com
PostgreSQL version: 14.0
Operating system:   windows
Description:

The following SQL has an unexpected syntax error

    SELECT DISTINCT ON (col) AS col, col2 FROM test

The AS clause is usually used to indicate alias, but it does not work in
this case

```
postgres=#
postgres=# SELECT version();
                          version
------------------------------------------------------------
 PostgreSQL 14.0, compiled by Visual C++ build 1914, 64-bit
(1 row)


postgres=# SELECT DISTINCT ON (col) AS col, col2 FROM test;
ERROR:  syntax error at or near "AS"
LINE 1: SELECT DISTINCT ON (col) AS col, col2 FROM test;
```

The following bug has been logged on the website:

Bug reference:      17232
Logged by:          Kyle Lahnakoski
Email address:      kyle@lahnakoski.com
PostgreSQL version: 14.0
Operating system:   windows
Description:       

The following SQL has an unexpected syntax error

    SELECT DISTINCT ON (col) AS col, col2 FROM test

The AS clause is usually used to indicate alias, but it does not work in
this case

On 2021-Oct-15, PG Bug reporting form wrote:

> The following SQL has an unexpected syntax error
> 
>     SELECT DISTINCT ON (col) AS col, col2 FROM test

Well, the "ON (col)" part is not an output column -- it's just the
specification of the column that you want distinctness over.  I suspect
you mean 

SELECT DISTINCT ON (col) col AS col, col2 FROM test

... which looks like a pretty bogus thing to do, since you have no say
on *which* values of col2 are you going to get for each distinct value
of col.  But ... it gives *some* result, at least.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Pensar que el espectro que vemos es ilusorio no lo despoja de espanto,
sólo le suma el nuevo terror de la locura" (Perelandra, C.S. Lewis)