Thanks very much, guys.

The problem i have is:

For example, the table customer have column customer_id and active. The customer_id is generated by an Oracle sequence. Usually we use customer_id and active in the WHERE clause. If I create a primary key on customer_id, I also need to create another index on customer_id and active.

The index created with primary key actually can help me nothing but slow the insert, delete. The sequence will make sure the unique of the customer_id.

What is your suggestion for this issue? Thanks.