Oracle 18c

By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.

CREATE TYPE my_sdo_geom_type AS OBJECT( 
  shape SDO_GEOMETRY, 

  MEMBER FUNCTION GetOrdinates(
    self IN my_sdo_geom_type,
    idx  IN NUMBER
  ) RETURN NUMBER
) 
/ 
CREATE TYPE BODY my_sdo_geom_type AS
  MEMBER FUNCTION GetOrdinates(
    self IN my_sdo_geom_type,
    idx  IN NUMBER
  ) RETURN NUMBER
  IS
  BEGIN 
  IF SIGN(idx) = 1 THEN
    return shape.sdo_ordinates(idx);
  ELSE
    return null; --temporarily returns null
  END IF;
  END;
END;
/ 
create table lines (my_sdo_geom_col my_sdo_geom_type);
insert into lines (my_sdo_geom_col) 
  values (my_sdo_geom_type(sdo_geometry('linestring(10 20, 30 40, 50 60)')));
1 rows affected

select (my_sdo_geom_col).GetOrdinates( 1) as first_ordinate,
       (my_sdo_geom_col).GetOrdinates(-1) as last_ordinate
from   lines


FIRST_ORDINATE
LAST_ORDINATE


10
null