plpgsql function

Hi,
creation of following function works just fine but usage not:):
mtldb=# select mtldb_wykonane(0);
ERROR:  unexpected SELECT query in exec_stmt_execsql()
Can You help me find an error?
tia

CREATE FUNCTION mtldb_wykonane (integer) RETURNS integer AS  '
   DECLARE
      zlecenie alias for $1;
      tls   integer;
      twz   integer;
   BEGIN
      SELECT count(*) as ls FROM serwery;
      tls:=new.ls;
      SELECT count(*) as wz FROM wykonanie
         WHERE zadanie_id=zlecenie AND kiedy IS NOT NULL;
      twz:=new.wz;

      if tls>twz
         RETURN -1;
      end if;
      if tls=twz
         RETURN 1;
      end if;
   END;
' LANGUAGE  'plpgsql' ;

Marcin Mazurek

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