CREATE TABLE test_g (
a timestamptz,
b timestamp GENERATED ALWAYS AS (a::timestamp) STORED
);
then an error occurred.
ERROR: 42P17: generation expression is not immutable
LOCATION: cookDefault, heap.c:2768
However the following 2 commands is ok.
CREATE TABLE test_i (
a int,
b bigint GENERATED ALWAYS AS (a::bigint) STORED
);
CREATE TABLE test_c (
a varchar,
b text GENERATED ALWAYS AS (a::text) STORED
);
I didn't get it. timestamptz changes then timestamp also changes. timestamp is part of timestamptz...
Even if column timestamptz is some value that is constantly changing (like now() ), it changes/updates then just in the mean time captures timestamp to column b.