I believe (and correct me if I am wrong) that the locate function on a
query component is processed by the application. That means that the
database will have to return all the records to the application, and
the component can then do a search for it. Even if the component does
use some form of binary search on the dataset, you have already paid a
performance penalty, especially if the database is on a different
machine and you have network speed to factor in.

The like operator will automatically try and use the available index.

select name
from employee
where name like 'A%'

will use the index on 'name', but

select name
from employee
where name like '%a'

can not use the index, and so doesn't.

Hope that helps

Adam.