I know how to do this with a trigger but investigating the [unlikely] possibility of doing it without one.
Can a column be forced to a predefined expression instead of just an overridable default one? I'm thinking something like:
`CREATE TABLE log(dt ALWAYS(datetime('now','localtime')),event);`
where `INSERT` or `UPDATE` of `dt` is either silently converted to `datetime('now')`, or allowed to be NULL if the column allows nulls.
This is a very common use case, and writing triggers seems like overkill.
(Does any popular database support this?)