Defines an extent index.
To specify that this is an extent index, use the following syntax:
Where name is the name of the index. It is useful to follow a naming convention so that indices can be easily distinguished from properties. For example, you could include IDX at the end of all index names.
Otherwise, omit this keyword or place the word Not immediately before the keyword.
If you are using bitmap indices, then an extent index is automatically added and there is no need to define one.