Обсуждение: aggregate function

Hello

I would like to know how can I define/create a new aggregate function. I
need a custom function that operate on a set of text strings and return a
certain string aggregate based on certain rules. But I cannot figure out how
can I define such a data set to operate on.

any hints?

cl.

"Claudio Lapidus" <clapidus@hotmail.com> writes:

> Hello
>
> I would like to know how can I define/create a new aggregate function. I
> need a custom function that operate on a set of text strings and return a
> certain string aggregate based on certain rules. But I cannot figure out how
> can I define such a data set to operate on.


Is this example helpful?

create function concat_agg_accum(varchar, varchar) returns varchar
    as 'select $1 || '', '' || $2'
    language sql
    strict immutable;

create aggregate concat_agg (
    basetype = varchar,
    stype = varchar,
    sfunc = concat_agg_accum
);

--
greg

Greg Stark wrote:
> Is this example helpful?

Yes, perfect! Thank you.
cl.

>
> create function concat_agg_accum(varchar, varchar) returns varchar
>     as 'select $1 || '', '' || $2'
>     language sql
>     strict immutable;
>
> create aggregate concat_agg (
>     basetype = varchar,
>     stype = varchar,
>     sfunc = concat_agg_accum
> );
>