Value-ordered NUSIs are very efficient for range conditions, and more so when strongly selective or when combined with covering. Because the NUSI rows are sorted by data value, it is possible to search only a portion of the index subtable for a given range of key values.
Value-ordered NUSIs have the following limitations.
- The sort key is limited to a single numeric or DATE column.
- The sort key column must be four or fewer bytes.
The following query is an example of the sort of SELECT statement for which value-ordered NUSIs were designed.
SELECT * FROM Orders WHERE o_date BETWEEN DATE '1998-10-01' AND DATE '1998-10-07';