Re: How to copy data between joined columns?

Bryce Nesbitt <bryce1@obviously.com> writes:
> If it were for the same rows in the same table, I would not have asked.
> This is for columns from two tables, whos relationship is only
> meaningful after a join.

You have to write out the join condition longhand, eg

UPDATE targettable SET targcol = srccol
FROM srctable
WHERE joincol1 = joincol2;

This can be tricky, particularly if there might be more than one source
row joining to a given target row.  (IIRC, the effective behavior is
that any given target row's update will occur against a random one of
the possible join partners.)  A lot of people prefer to code it using
sub-selects.
        regards, tom lane