RECREATE TABLE T(
  ID INT NOT NULL,
  ID_FATHER INT,
  ID_MOTHER INT,
  COST NUMERIC(15, 2),
  CONSTRAINT PK_T PRIMARY KEY(ID),
  CONSTRAINT FK_T_FATHER FOREIGN KEY (ID_FATHER) REFERENCES T(ID),
  CONSTRAINT FK_T_MOTHER FOREIGN KEY (ID_MOTHER) REFERENCES T(ID)
);

EXECUTE BLOCK (ID INT = :ID)
AS
DECLARE CURRENT_ID INT;
DECLARE ID_FATHER INT;
DECLARE ID_MOTHER INT;
DECLARE COST INT;
DECLARE DEPTH INT;
BEGIN
  FOR
    WITH RECURSIVE R AS (
      SELECT ID,
             ID_FATHER,
             ID_MOTHER,
             COST,
             0 AS DEPTH
      FROM T
      WHERE ID = :ID
      UNION ALL
      SELECT
        T.ID,
        T.ID_FATHER,
        T.ID_MOTHER,
        T.COST,
        R.DEPTH + 1
      FROM R
        JOIN T ON T.ID = R.ID_FATHER
      UNION ALL
      SELECT
        T.ID,
        T.ID_FATHER,
        T.ID_MOTHER,
        T.COST,
        R.DEPTH + 1
      FROM R
        JOIN T ON T.ID = R.ID_MOTHER
    )
    SELECT ID,
           ID_FATHER,
           ID_MOTHER,
           COST,
           DEPTH
    FROM R
    INTO CURRENT_ID,
         ID_FATHER,
         ID_MOTHER,
         COST,
         DEPTH
  DO BEGIN
    /* алгоритм расчёта */
  END
END