Re: Functions returning multiple rowsets

On Mon, Sep 28, 2009 at 2:05 PM, Merlin Moncure <mmoncure(at)gmail(dot)com> wrote:
> On Mon, Sep 28, 2009 at 12:49 PM, Thom Brown <thombrown(at)gmail(dot)com> wrote:
>> Hi,
>>
>> Is it possible to create a function using 'SQL' as language which could
>> return multiple rowsets, such as "SELECT * FROM TABLE1; SELECT * FROM
>> TABLE2;" where both results are returned in the output?  I know this can be
>> done in stored procedures in other RBDMS but can this be done in a function?
>
> you have a couple of approaches:
> *) declare refcursors inside the function and references them later in
> the transaction
> *) make temp tables
> *) arrays:
> create function two_sets(_foos out foo[], _bars out bar[]) returns record as
> $$
>  select array(select foo from foo), array(select bar from bar);
> $$ language sql;
>
> with s as (select * from two_sets()),
> foo as (select unnest(_foos) from s),
> bar as (select unnest(_bars) from s)
> select
>  (select count(*) from foo) as no_foos,
>  (select count(*) from bar) as no_bars;

I should mention the query above only works in 8.4+. the array
approach generally only works as of 8.3 and has limits (don't return
billion records). Also, it's not good style (IMO) to name 'with'
expressions same as actual tables:

with s as (select * from two_sets()),
f as (select unnest(_foos) from s),
b as (select unnest(_bars) from s)
select
(select count(*) from f) as no_foos,
(select count(*) from b) as no_bars;

is cleaner.

merlin