postgresql - Return 0 or 1 rows from function -

is possible function return 1 record, return 0 records if there empty result set. example:

if have empty table contains no data...

create table foo (     fooid serial constraint pk_foo primary key,     foovalue integer not null );

... , function ...

create or replace function get_onefoo() returns foo $$     select         fooid,         foovalue             foo     limit 1 $$ language sql;

... ...

select get_onefoo()

... results in ...

total query runtime: 11 ms. 1 row retrieved.

... ...

select     fooid,     foovalue     foo limit 1

... results in ...

total query runtime: 10 ms. 0 rows retrieved.

returns setof foo

in instead of

returns foo

the later returns composite type:

IO