Why can't I reference a user defined type field when using nested queries?

Question

So I have the following user defined type in my oracle database:

CREATE OR REPLACE TYPE METRIC_IMPERIAL_DISTANCE AS OBJECT
(
  METERS_FEET INTEGER,
  CENTIMETERS_INCHES INTEGER,
  FRACTION NUMBER
)

I can do the following:

SELECT t_id, get_distance_breakdown (h.height, h.unit_of_measure_id) height_breakdown
        FROM   heights h

and even

SELECT t_id, get_distance_breakdown (h.height, h.unit_of_measure_id).meters_feet height_meters_feet
        FROM   heights h

but the following fails with a ORA-00904: "HEIGHT_BREAKDOWN"."METERS_FEET": invalid identifier error:

SELECT t_id, height_breakdown.meters_feet
FROM   (SELECT t_id, get_distance_breakdown (h.height, h.unit_of_measure_id) height_breakdown
        FROM   heights h);

What gives? If there isn't some simple and obvious work-around for this then that decimates much of what would be useful about oracle's user defined types. I feel like I must be missing something.

Answer 1

I believe Oracle needs an alias for the in-line view:

SELECT v.t_id, v.height_breakdown.meters_feet
FROM   (SELECT t_id, get_distance_breakdown (h.height, h.unit_of_measure_id) height_breakdown
        FROM   heights h) v;