tricky sql question

Does anyone know a nifty way of writing an update sql where the qualifying rows are determined by matching the multicolumn prime key with values returned from a subselect. This is one way, but it this way oracle doesn't use any indexes:

update tbl_a set some_column = value
where key1 || key2 in (select key1 || key2 from tbl_b where other_column = xyz )

on a select I could do a join:

select some_column
from tbl_a a, tbl_b b
where a.key1 = b.key1
and a.key2 = b.key2
and b.other_column = xyz

key1 and key2 are not necessarily keys for tbl_b, they just match in type the prime key columns of tbl_a. Received on Tue May 27 1997 - 00:00:00 CDT