I have two sizable (~1M rows each) Oracle tables that I need to join on a range of integers. For example,

Range_Descriptors
-----------------
range_id
from_value number(38)
to_value number(38)
descriptor

Values
------
value_id 
value number(38)
...

And so in this case I need to get the Range_Descriptors.descriptor for each record in Values where value falls between from_value and to_value.

The most obvious query does return the expected results; however, it runs extremely slowly (~20 minutes):

select v.value_id, r.descriptor
from Values v join Range_Descriptors r on v.value between r.from_value and r.to_value;

I’ve played around with different indexing options, but I haven’t found anything that significantly improves performance. Currently there are indexes on Range_Descriptors(from_value, to_value) and on Values(value). Suggestions?