Re: Should we document how column DEFAULT expressions work?

On 01.07.24 01:54, David Rowley wrote:
> On Thu, 27 Jun 2024 at 23:57, Peter Eisentraut <peter(at)eisentraut(dot)org> wrote:
>> Maybe we should really be thinking about deprecating these special
>> values and steering users more urgently toward more robust alternatives.
>>
>> Imagine if 'random' were a valid input value for numeric types.
>
> I think there are valid reasons to use the special timestamp input
> values. One that I can think of is for use with partition pruning. If
> you have a time-range partitioned table and want the planner to prune
> the partitions rather than the executor, you could use
> 'now'::timestamp in your queries to allow the planner to prune.

Yeah, but is that a good user interface? Or is that just something that
happens to work now with the pieces that happened to be there, rather
than a really designed interface?

Hypothetically, what would need to be done to make this work with now()
or current_timestamp or something similar? Do we need a new stability
level that somehow encompasses this behavior, so that the function call
can be evaluated at planning time?

> That
> works providing that you never use that in combination with PREPARE
> and never put the query with the WHERE clause inside a VIEW.

And this kind of thing obviously makes this interface even worse.