My initial response to what this DBA has told you was he is wrong. I then did a search on the Oracle Technology Network, and it looks like he may still be wrong. The closest to your question I could find can be found here

>Hi,
>
>I have a VFP app that will have to make Selects on an Oracle table, containing something like 28 milion records. I'll have to look for records that will have a numeric field greater than a specified value:
>

>Select * From OracleTable Where Field >= Value
>

>Looking at that table's indices I could notice that there was no index for "Field", then I asked the DBA to create one for it. He responded to me it would be useless to create such an index because Oracle would ignore it (even if it existed) and would perform a full scan (!) in that table for the select (above). The reason he told me is that: "if you create and index for an Oracle table refering just one field of that table and the comparison operation in the Select is a ">" or a ">=" the indices would be ignored and a full scan will be performed".
>
>Is that so?
>
>Fernando