On 11/15/19 12:57 PM, John Lumby wrote:
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.
Seems you are looking for Serializable Isolation Level:
https://www.postgresql.org/docs/11/transaction-iso.html#XACT-SERIALIZABLE
Though the above results in a rollback.
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
--
Adrian Klaver
adrian.kla...@aklaver.com
