catch an 'update where false' ? - Mailing list pgsql-sql

hello

I' trying to catch un update that fails to update because no row matchs
the where clause:

for instance:
update t set c=1 where cc=2;
--and no row with cc=2

I would like to perform a
insert into t (c) values 1;
before the update is resolved

I hoped a trigger before update could help me, but it seems
that if where clause evals to false, triggers are not called..

someone knows a way around this ?

thanks