Consider the following query:

SELECT *
FROM FLIGHTS
WHERE orig_airport < 'BBB'
AND orig_airport <> 'AKL'

The second predicate is not optimizable, but the first predicate is. The second predicate becomes a qualification for which Derby evaluates the entries in the index as it traverses it.

• The following comparisons are valid qualifiers:
  • =
  • <
  • <=
  • >
  • >=
  • IS NULL
  • BETWEEN
  • LIKE
  • <>
  • IS NOT NULL
• The qualifier's reference to the column does not have to be a simple column reference; you can put the column in an expression.
• The qualifier's column does not have to be the first column in the index and does not have to be contiguous with the first column in the index.