No value resolution for non-deterministic defaults

Values like nextval and current_timestamp are non-deterministic. For those values, default call chains are not properly resolved.

create sequence s;

create table t(x int default (nextval(s)), y int default(x));

insert t(x) values (default);

insert t(y) values (default);

We would expect the value of 2 inserted to y on the second insert, but instead we'll have NULL:

select * from t;

x       y

1       1

2       NULL

Example with current_timestamp:

create table t(x timestamp default current_timestamp, y timestamp default(x));

insert t(x) values (default);

insert t(y) values (default(y));

select * from t;

x       y

2025-06-27 14:40:43     2025-06-27 14:40:43

2025-06-27 14:40:43     NULL

For non-deterministic expressions, we'd have to make defaults a part an expression resolution tree, like it's done for vcols. Here instead, a value for y is fetched before x is calculated.

For deterministic expressions, the value is stored in the default_values record and is restored before each insert. For non-deterministic defaults, the value of NULL is stored there.