It seems to me that UPDATE is well designed for constants, and functions that do not
depend on the database, but when I want to UPDATE based on a table, I run into trouble.
See, this is not allowed:
mysql> update address set membersince = (select membersince from address where memberid
> = 1258) where memberid = 1724;
An intermediat variable is the only way, right? And sometimes I want to change many of a
field from another table: I read that subqueries are to be avoided, but in this case I
cannot find any means other than correlated subquery to do that. Eh?