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From "Yip Ng" <yipng...@gmail.com>
Subject Re: Functions in GROUP BY expressions? (related to DERBY-883)
Date Tue, 31 Oct 2006 23:00:21 GMT
On 10/31/06, Army <qozinx@gmail.com> wrote:
>
> Many thanks to all who took the time to provide clarifications in this
> thread.
> At this point I think the only question I have remaining is with respect
> to
> something Dan wrote in one of his replies, namely:
>
> > the grouping by functions does not work because at the moment Derby
> > assumes all functions are non-deterministic.
>
> Note the use of the word "all".
>


I think what Dan meant was that all *user defined functions* defined via
CREATE FUNCTION statement are assumed to be non-deterministic since users
cannot declare a function as deterministic in the current implementation of
Derby, so implicitly, they are non-deterministic.

For built-in functions such as SUBSTR, LTRIM and RTRIM, I believe they are
deterministic since they always return the same result from successive
invocations with identical input(s)
and they work as expected with group by expression.

For SIN, COS, TAN functions,  they are also considered deterministics.
However, they do not work currently in Derby with group by expression as
they are mapped to  JavaToSQLValueNode and such nodes always return false in
isEquivalent() method, so I think this is an implementation restriction for
those built-in functions.

Perhaps it is a good idea to have documentation that describes the function
determinism of all built-in functions in the reference manual.


Regards,
Yip Ng

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