Re: count (DISTINCT expression [ , ... ] ) and documentation

2008/12/26 Ivan Sergio Borgonovo <mail(at)webthatworks(dot)it>:
> On Fri, 26 Dec 2008 15:46:48 +0100
> "Pavel Stehule" <pavel(dot)stehule(at)gmail(dot)com> wrote:
>
>> count has only one argument,
>
> then what was changed between 8.1 and 8.2 to change the docs?
> None of the functions listed in:
> http://www.postgresql.org/docs/8.2/static/functions-aggregate.html
> seems to support
> aggregate(distinct exp [,exp])

http://www.postgresql.org/docs/8.2/interactive/functions-aggregate.html

http://www.postgresql.org/docs/8.2/interactive/functions-aggregate.html#FUNCTIONS-AGGREGATE-STATISTICS-TABLE

>
> Does the change reflect the change in the possibility to write user
> defined aggregates that support more then one distinct expression?

CREATE AGGREGATE name ( input_data_type [ , ... ] ) (
SFUNC = sfunc,
STYPE = state_data_type
[ , FINALFUNC = ffunc ]
[ , INITCOND = initial_condition ]
[ , SORTOP = sort_operator ]
)

you are able to write multi param aggregates.

regards
Pavel Stehule

>
> The first thing that comes to my mind to emulate
> count(distinct a,b)
> would be to
>
> create table test.dist (a int, b int);
> insert into test.dist values(1,0);
> insert into test.dist values(1,0);
> insert into test.dist values(1,1);
> insert into test.dist values(0,0);
> select count(*) from (select distinct a,b from test.dist ) a;
>
> but still I can't think of anything that would work with
> aggregate(distinct a,b)
> not just count.
>
> --
> Ivan Sergio Borgonovo
> http://www.webthatworks.it
>
>
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