Re: Trigger with conditional predicates

> On Jan 1, 2021, at 07:56, Dirk Mika <Dirk.Mika@mikatiming.de> wrote:
> In particular, columns are populated with values if they are not specified in the update statement which is used.
> Usually with an expression like this:
>
>      IF NOT UPDATING('IS_CANCELED')
>      THEN
>         :new.is_canceled := ...;
>      END IF;
>
> I have not found anything similar in PostgreSQL. What is the common approach to this problem?

PostgreSQL doesn't have an exact equivalent.  Typically, the OLD and NEW values are compared and then action is taken
basedon that.  For example, in PL/pgSQL: 

IF NEW.is_canceled IS NOT DISTINCT FROM OLD.is_canceled THEN
    NEW.is_canceled := etc etc ;
ENDIF;

There's currently no way to detect if the column was simply not mentioned at all in the UPDATE statement.

--
-- Christophe Pettus
   xof@thebuild.com