Steve,

Tore already gave you the answer. I'd also add that write the expression like you'd see in an algebra text ( 10 < a < 15 ) in a SQL statement won't fully optimize:

select sum(b) ;
   from x ;
   where 10 < a and a < 15

10 < a won't optimize because the field is on the right hand side of the operator. a > 10 will optimize.

>The actual implementation of this example involves a much more complicated scenario, but I think this expresses the heart of my question.
>
>Calculate sum(b) for a > 10 and a < 15 to m_sum_b
>
>Will execution be speeded up if a is indexed?