/* Объекты, дерево обычное ... */
CREATE TABLE OBJECTS (
    ID         INTEGER NOT NULL,
    PID        INTEGER
    ...
);
ALTER TABLE OBJECTS ADD CONSTRAINT PK_OBJECTS PRIMARY KEY (ID);
ALTER TABLE OBJECTS ADD CONSTRAINT FK_OBJECTS_1 FOREIGN KEY (PID) REFERENCES OBJECTS (ID) ON DELETE CASCADE ON UPDATE CASCADE;

INSERT INTO OBJECTS VALUES(1, NIL); 
INSERT INTO OBJECTS VALUES(2, NIL); 
INSERT INTO OBJECTS VALUES(3, NIL); 
INSERT INTO OBJECTS VALUES(4, 3); 
INSERT INTO OBJECTS VALUES(5, 4); 

/* ... и расстояния между ними */ 
CREATE TABLE DISTANCES (
    ID         INTEGER NOT NULL,
    IDFROM     INTEGER,
    IDTO       INTEGER
    ...
);
ALTER TABLE DISTANCES ADD CONSTRAINT PK_DISTANCES PRIMARY KEY (ID);

INSERT INTO DISTANCES VALUES(1, 1, 3); 
INSERT INTO DISTANCES VALUES(2, 2, 3); 
INSERT INTO DISTANCES VALUES(3, 3, 4); 
INSERT INTO DISTANCES VALUES(4, 3, 5); 

create or alter procedure GET_CD_CNT(
    PARNT integer)
returns (
    OCHILDS integer,
    ODISTS integer)
as
declare variable ID integer;
declare variable VCHILDS integer;
declare variable VDISTS integer;
begin

  PARNT = COALESCE(PARNT,  0);
  OCHILDS = 0;
  ODISTS  = 0;

  SELECT COUNT (1) FROM DISTANCES D WHERE (D.IDFROM = :ROOT) OR (D.IDTO = :PARNT) into :ODISTS;

-- INSERT INTO GTT_DIST 
--   SELECT D.ID FROM DISTANCES D WHERE (D.IDFROM = :PARNT) OR (D.IDTO = :PARNT) 

  for SELECT R.ID FROM OBJECTS R WHERE COALESCE(R.PID,  0) = :ROOT into :ID
  do
  begin
    SELECT G.OCHILDS, G.ODISTS FROM GET_CD_CNT(:ID) G into :VCHILDS, :VDISTS;
    OCHILDS = OCHILDS + VCHILDS + 1;
    ODISTS  = ODISTS  + VDISTS;
  end
  suspend;
end

SELECT COUNT DISTINCT(G.ID) FROM GTT_DIST G

with recursive
TREE as (
  select ID, PID from OBJECTS where ID = :PID -- PID = :PID 
  union all
  select ID, PID from OBJECTS O
  inner join TREE T on O.PID = T.ID
)
select count(distinct D.ID) from DISTANCES D
inner join TREE T on D.IDFROM = T.ID or D.IDTO = T.ID