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

Tom, any status on this DISTINCT ON ripout?


> Hannu Krosing <hannu@trust.ee> writes:
> >> "DISTINCT will eliminate all duplicate rows from the selection.
> >> DISTINCT ON column will eliminate all duplicates in the specified column;
> >> this is equivalent to using GROUP BY column."
> 
> > If it is equivalent to GROUP BY then it should allow only aggregates 
> > in non-distinct columns, like:
> > select distinct on date date, sum(bytes) from access_log;
> > If it does not, then it should be files as a bug imho.
> 
> It does not.  Whether that is a bug is hard to say, since there is no
> standard I know of that says what it *is* supposed to do.
> 
> If you look at the select_distinct_on regress test outputs, I bet you
> will be even less happy:
> 
> QUERY: SELECT DISTINCT ON string4 two, string4, ten
>        FROM tmp
>    ORDER BY two using <, string4 using <, ten using <;
> two|string4|ten
> ---+-------+---
>   0|AAAAxx |  0
>   0|HHHHxx |  0
>   0|OOOOxx |  0
>   0|VVVVxx |  0
>   1|AAAAxx |  1
>   1|HHHHxx |  1
>   1|OOOOxx |  1
>   1|VVVVxx |  1
> (8 rows)
> 
> That's not exactly my idea of "distinct" values of string4 ---
> but apparently whoever made up the regress test thought it was OK!
> 
> Can anyone defend this feature or provide a coherent definition
> of what it's supposed to be doing?  My urge to rip it out is
> growing stronger and stronger...
> 
>             regards, tom lane
> 
> 


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