Assume I have a book table defined as follows:
table book(id varchar(50), title varchar(100),type varchar(20),publisher varchar(20), price float)
Suppose an index is defined on ID. Now queries which uses the ID will be improved, like:
select * from book where id='abcd123456'
But will queries that uses other fields be improved as well? For instance, these two queries:
select * from book where title = 'algorithms'
select * from book where price > 25