Multi field Indexes in SQL

[Stephen McMillan]

I'm wanting to update or delete records in one table using a multi field index
obtained from the results from a subquery.

An example of what I have done in the past is:

Delete
From Table1
Where Key1||Key2||Key3 in (
Select FieldA||FieldB||FieldC
From Table2
Where FieldD = 0);

Is there a better way on Oracle 7.3.4?