Re: [HACKERS] Re: [HACKERS] generated columns

On 12/31/2017 09:38 AM, Peter Eisentraut wrote:
> On 12/30/17 16:04, Joe Conway wrote:
>> +<para>
>> + The generation expression can refer to other columns in the table, but
>> + not other generated columns.  Any functions and operators used must be
>> + immutable.  References to other tables are not allowed.
>> +</para>
>> 
>> Question -- when the "stored" kind of generated column is implemented,
>> will the immutable restriction be relaxed? I would like, for example, be
>> able to have a stored generated column that executes now() whenever the
>> row is written/rewritten.

<snip>

> Maybe some of this could be relaxed at some point, but we would have to
> think it through carefully.  For now, a trigger would still be the best
> implementation for your use case, I think.

Sure, but generated column behavior in general can be implemented via
trigger.

Anyway, I have seen requests for change data capture
(https://en.wikipedia.org/wiki/Change_data_capture) in Postgres which is
apparently available in our competition without requiring the use of
triggers. Perhaps that is yet a different feature, but I was hopeful
that this mechanism could be used to achieve it.

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