Re: Problem using Subselect results

I did try the following:

SELECT DISTINCT ON (two.two_id) two.two_value FROM one,two WHERE
(one.two_id=two.two_id
AND one.updatenr > two.updatenr) ORDER BY two.updatenr ASC;

I thought this would
a) order the result list by updatenr
b) return the first record only for records that are equal on the two.two_id
field
which would return exactly what I need - return the record with the

But what I get instead is "ERROR: SELECT DISTINCT ON expressions must match
initial ORDER BY expressions" *grrrmpfh*

But after a while playing around I noticed that the "initial" in that sentence
above is important - adding two.two_id as first argument to the ORDER BY does
not change the result but fulfill the requirements - the expressions don't have
to be excactly the same - just the initial argument.

My view which returns the (hopefully) correct results:

SELECT DISTINCT ON (two.two_id) two.two_value FROM one, two WHERE ((one.two_id
= two.two_id) AND (one.updatenr > two.updatenr)) ORDER BY two.two_id,
two.updatenr;

Next step is to include corresponding information from table three - now I need
subselects right? no way around with this DISTINCT and ORDER by stuff in it ...

Many thanks for your help so far,
Oliver

Quoting Oliver Heinz <oheinz(at)stud(dot)fbi(dot)fh-darmstadt(dot)de>:

> I'll try this tomorrow - combining DISTINCT ON (two.two_id) and sorting by
> two.updatenr could (should) have the desired effect - I never thought about
> using ORDER and DISTINCT that way.
>
> I'll report my success or failure...
>
> Thanks so far!
>
> Bye,
> Oliver

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