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