Re: [SQL] Re: [HACKERS] SELECT DISTINCT question

Oleg Bartunov <oleg(at)sai(dot)msu(dot)su> writes:
> thanks, this works. But why parser complains about such query:

> discovery=> select distinct on a.date a.date, a.bytes from access_log a;
> ERROR: parser: parse error at or near "."

Probably the grammar specifies just <column name> and not anything
more complex after DISTINCT ON. It'd be risky to try to accept a
general expression after ON, due to the silly decision to leave out
any terminating punctuation.

>> SELECT DISTINCT ON is not in SQL92, and I think it shouldn't be in
>> Postgres either...

> I'm not an SQL expert, but if it works and this feature is in standard
> but only syntax is diffrent,

No, there is no feature in SQL that allows DISTINCT on a subset of
columns, period. This is not merely a matter of syntax, it's a
fundamental semantic issue.

> why just not to use standard
>
> select distinct(date), bytes from access_log;
>
> Or I'm missing here ?

I don't think that does what you expect it to (hint: the
parentheses are redundant).

regards, tom lane