To reiterate what Luis said, if you have this huge multicolumn table, but
the columns you need are all in the index it will only access the index
and never touch the physical. For example, suppose you have a state index
(custbystate) on your customer master and you run this sql:
select state, count(*)
from custmast
group by state
order by state
then it will only access custbystate. See iNav's Visual Explain.
Now if you do something like
select state, max(custno), count(*)
from custmast
group by state
order by state
then it's going to need the physical since custno is not stored in the
index.
Rob Berendt
