Do note the headline is written in jest! Of course if you create a database index, you should try to make use of it in order to allow your queries to return the results faster. However, if you write your query in such a manner as below:
a.field1, a.field2, b.field3
c.field1 = a.field1
Apparently in Oracle, it is still possible to create a function-based index to meet this shortfall, but in SQL Server you will need to specially create a computed column, then create an index specifically for that column in order to enjoy the benefits of an index!