Re: Seamless replacement to MySQL's GROUP_CONCAT function...

2013/8/6 Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>:
> Pavel Stehule escribió:
>
>> you code can be translated to
>>
>> CREATE OR REPLACE
>> FUNCTION GROUP_CONCAT_ATOM(field1 TEXT, field2 TEXT, delimiter TEXT)
>> RETURNS TEXT AS $$
>> BEGIN
>> RETURN COALESCE(field1||delimiter||field2, field2, field1);
>> END;
>> $$ LANGUAGE plpgsql;
>
> Actually you don't even need plpgsql for this, do you ..

There is better optimized plpgsql - not sure, why - probably, so there
is not possible inlining .. and start of SQL engine is little bit
slower than start of plpgsql.

postgres=# create table f(a text, b int);
CREATE TABLE
postgres=# insert into f select 'Ahoj', random()*100 from
generate_series(1,10000);

select group_concat(a,',') from f group by b;

PL/pgSQL .. 36 ms
SQL .. 49 ms

Regards

Pavel Stehule

>
> --
> Álvaro Herrera http://www.2ndQuadrant.com/
> PostgreSQL Development, 24x7 Support, Training & Services