HP 3000 Manuals

ALLBASE/SQL Performance Guidelines

Using Predicates with BETWEEN 

For the BETWEEN clause, the optimizer makes the decision depending on the
following (among other things):

   *   The range of the BETWEEN.
   *   The range of the HIGH and LOW values of the index column(s).

For example, if the range in the BETWEEN predicate is very wide relative
to the HIGH and LOW values stored in the index, the optimizer expects a
large number of rows to be returned and is therefore more likely to
choose a serial scan.  (Note that the optimizer assumes a uniform
distribution of values.)  In the case of BETWEEN predicates with host
variables, the actual range of values cannot be known until run time, so
the optimizer uses default selectivity values.

MPE/iX 5.0 Documentation