[HACKERS] ALTER composite type does not work, but ALTER TABLE which ROWTYPE is used as a type - works fine

[Dmitry Koterov]

Hello.

I can successfully ALTER a NON-EMPTY table (ct) which ROWTYPE is used as a
column type for another table (dt):

CREATE TABLE ct (id INTEGER);
CREATE TABLE dt (id INTEGER, c ct);

INSERT INTO dt VALUES(1, '(666)');
SELECT * FROM dt;
-- (1, '(666)')

ALTER TABLE ct ADD COLUMN n INTEGER;
SELECT * FROM dt;
-- (1, '(666,)')

You see, '(666,)' means that the new field is added successfully.


But, if I declare ct as a COMPOSITE type (not a table), it is not permitted
to ALTER this type (Postgres says that there are dependensies on ct).
Why?