As you learned in the previous section, Derby might be able to use an index on a column to find data more quickly. If Derby can use an index for a statement, that statement is said to be optimizable. The statements shown in the preceding section allow Derby to use the index because their WHERE clauses provide start and stop conditions. That is, they tell Derby the point at which to begin its scan of the index and where to end the scan.
For example, a statement with a WHERE clause looking for rows for which the orig_airport value is less than BBB means that Derby must begin the scan at the beginning of the index; it can end the scan at BBB. This means that it avoids scanning the index for most of the entries.
SELECT * FROM Flights WHERE flight_id = 'AA1111' AND segment_number <> 2