deadlock в процедуре: почему?

update zzz set zr = :sum_tmp where id = :idd;

CREATE PROCEDURE NEW_PROCEDURE 
RETURNS (
    IDD INTEGER)
AS
DECLARE VARIABLE SUM_TMP INTEGER;
DECLARE VARIABLE SUM1 INTEGER;
DECLARE VARIABLE IDM INTEGER;
begin

 for select t.idclient from table1 t order by 1 desc into :idm
  do
   begin
    select zt.zr from zzz zt where zt.id=:idm into :sum1;
    for select DID from getparents (:idm) where DID<>:idm into :idd
     do
      begin
       select zt.zr from zzz zt where zt.id=:idd into :sum_tmp;
       sum_tmp = :sum_tmp-sum1;
       update zzz set zr = :sum_tmp where id = :idd;
      end
   end

end

for select t.idclient from table1 t order by 1 desc into :idm
  do
   begin
    select zt.zr from zzz zt where zt.id=:idm into :sum1;

for select t.idclient,zt.zr from table1 t left join zzz zt
 on zt.id=t.idclient
 order by 1 desc into :idm,:sum1;