Adrian Klaver wrote :
>
> On 11/15/19 10:37 AM, John Lumby wrote:
>
> > Suppose the original statement is
>
> > UPDATE myview VW set VW.counter = 11 where VW.primary_key = xxxx and
> > VW.counter = 10;
>
> > and my trigger constructs this statement
>
> > UPDATE basetable BT set BT.counter = 11 where BT.primary_key =
> > OLD.primary_key;
>
> Not following.
>
> Do you want OLD.primary_key set to 11 or BT.counter set to 12/both/or
>
> some other action?
Sorry I did not make it clear.
I want some way for the trigger to discover and apply any predicates *other*
than
primary key equality condition that were applied to the original statement,
which in the example is
VW.counter = 10
(the repeated AND in the original append's example was a typo, corrected above)
so for this example I want the trigger to build a statement reading
UPDATE basetable BT set BT.counter = 11 where BT.primary_key = xxxx and
BT.counter = 10;
where xxxx is the value of OLD.primary_key
so that, if some other transaction had updated BT.counter to some other value
such as 11
in that tiny window I described in previous append,
the result of the generated statement would be no rows updated and a return TAG
of 0 rows.
The significance being that the original application would be able to discover
that its update was not applied based on this return TAG
(actually the trigger returns a null tuple to indicate this).
>
> > Cheers, John
>
> Adrian Klaver
>
> adrian.kla...@aklaver.com
>
