Re: Auto-updated fields

Zoltan Boszormenyi írta:
> Martijn van Oosterhout írta:
>> On Wed, May 07, 2008 at 03:04:49PM -0700, David Fetter wrote:
>>
>>> 1. Create a generic (possibly overloaded) trigger function, bundled
>>> with PostgreSQL, which sets a field to some value. For example, a
>>> timestamptz version might set the field to now().
>>>
>>
>> Doesn't the SQL standard GENERATED BY functionality work for this? Or
>> won't that handle updates?
>>
>
> You mean GENERATED ALWAYS AS (expression)?
> Yes, they should be updated on every UPDATE as the expression
> may include other fields in the same row.
>
> A GENERATED column implemented as a stored column would
> work for this but a virtual column would not. A virtual column
> would return different values for "now()" in every SELECT.
>
> However we can argue for use cases of a virtual column and implement
> it similarly as VIEWs, i.e an ON SELECT rule can expand the original
> expression of the column definition.
>
> I suggest using these syntaxes if we decide to implement them:
>
> GENERATED ALWAYS AS (expression) -- SQL standard stored GENERATED column
> GENERATED VIRTUAL AS (expression) -- virtual column, obviously

Or, as found in Oracle 11g:

GENERATED ALWAYS AS (expr) VIRTUAL

>
>> Have a nice day,
>>
>
> Best regards,
> Zoltán Böszörményi
>

--
----------------------------------
Zoltán Böszörményi
Cybertec Schönig & Schönig GmbH
http://www.postgresql.at/