On Friday, April 11, 2025, Tom Lane <
tgl@sss.pgh.pa.us> wrote:
jian he <jian.universality@gmail.com> writes:
> CREATE TABLE gtest1 (a int, b int GENERATED ALWAYS AS (a * 2) STORED);
> CREATE VIEW gtest1v AS SELECT * FROM gtest1;
> ALTER VIEW gtest1v ALTER COLUMN b SET DEFAULT 100;
> INSERT INTO gtest1v VALUES (8, DEFAULT) returning *;
> ERROR: cannot insert a non-DEFAULT value into column "b"
> DETAIL: Column "b" is a generated column.
> we can make
> ALTER VIEW gtest1v ALTER COLUMN b SET DEFAULT 100;
> error out,
This is not an improvement over having the error happen at run time.
(1) What if the state of the underlying column changes between the
ALTER VIEW and the INSERT? Either you have rejected something
that could have worked, or in the other direction you're going to get
the run-time error anyway.
I concur. The view is only loosely coupled to the base relation, via the rewrite rule which is applied at runtime. Putting checks in place that strongly couples the two relations adds a coupling burden that we are better off avoiding.
David J.
