Re: Update with join ignores where clause - updates all rows

"Brian" <bengelha(at)comcast(dot)net> writes:
> The same join here, updates every row in the table which is incorrect.

> update
> dw.prints_by_hour
> set
> count = h.count + w.count
> from
> dw.prints_by_hour_work w , dw.prints_by_hour h
> WHERE
> w.year = h.year
> and w.month = h.month
> and w.day = h.day
> and w.hour = h.hour

No, it's not a bug: it's a self-join. If we identified the target table
with the "h" table then it would be impossible to do self-joins in
UPDATE.

You need to write

update
dw.prints_by_hour
set
count = dw.prints_by_hour.count + w.count
from
dw.prints_by_hour_work w
WHERE
w.year = dw.prints_by_hour.year
and w.month = dw.prints_by_hour.month
and w.day = dw.prints_by_hour.day
and w.hour = dw.prints_by_hour.hour

There's been some talk of allowing an alias to be attached to the target
table ("update dw.prints_by_hour h") which would make it possible to
write the update a bit more compactly, but we haven't done that.

regards, tom lane