Sometimes a table scan is the most efficient way to access data, even if
a potentially useful index is available. For example, if the statement returns
virtually all the data in the table, it is more efficient to go straight to
the table instead of looking values up in an index, because then
For example:
In the Flights table, most of the airport codes
begin with letters that are less than Z. Depending
on the number of rows in the table, it is probably more efficient for
Only a few flights have airport codes that begin with a letter less than B.