Forced Use of Secondary Indexes
You can force a secondary index to be used by referencing it in the query, but the optimizer must ensure that this is never necessary. For example, consider the following query:
select * from emp
where emp.name = 'Shigio';
To force it to use a secondary index, change it to the following:
select * from emp, xname
where xname.tidp = emp.tid
and xname.name = 'Shigio';