Subject Identity vs Before Insert Trigger
Author Daniel Miller
The fault or misunderstanding is probably mine, but:

I thought the "identity" definition was functionally the same as the
before-insert with generator. Particularly with regards to handling null
values during inserts. However, given:

create table TEST1 (
TEST_ID integer generated by default as identity primary key
TEST_NAME varchar(10)

Attempting to execute:

update or insert into TEST1 (TEST_ID, TEST_NAME)
values (null, 'abc') matching (TEST_ID)

results in:
validation error for column "TEST1"."TEST_ID", value "*** null ***".

However, the same query works without issue with a before-insert trigger
using a generator. My question - is this intended behavior? Or a bug in
the identity implementation?