Conditions in UPDATE statements

This is kind of a fix to common developer misuse. I noticed that sometimes see the solution for searching more complex constructs as this:

[..] where f1||f2||f3 in (select f1||f2||f3 from t1)

While in SELECT this is simply weird, because one may simply join 2 tables and specify conditions with f1=f1 etc., it may be considered when we play with DML. Of course this means the optimizer can not use indexes (unless there is some rather complex index on expression), but developers forget about very easy construct:

[..] where (f1, f2, f3) in (select f1, f2, f3 from t1)

Now plans look much better and we still may create condition on several fields at once.