Re: left join with smaller table or index on (XXX is not null) to avoid upsert

the only difference here is, that the trigger will memcmp (compare)
all data. Say, if we have two columns, int and bytea, and just want to
compare fist one - it will use a lot of cpu in vain.
I have to say, it is a shame sometimes - that trigger isn't aware of
what fields we do update exactly