Вот так попробуй

CREATE OR REPLACE FUNCTION public.table_count(TEXT)
RETURNS int4 AS
'
DECLARE
table_ ALIAS FOR $1;
c_ INTEGER;
query TEXT;
rec_ RECORD;

BEGIN
query := \' select count(*) as _count from \'||table_ ;

FOR rec_ IN EXECUTE query LOOP
c_:=rec_._count;
END LOOP;
RETURN c_;
END;
'
LANGUAGE 'plpgsql' VOLATILE;

select * from table_count ('table1');

Некрасиво - зато работает