I'm curious what impact Indexes have on the performance of MySQL and ultimately my website...

For example, what is the "cost" of a Standard Index in MySQL?

And what is the "cost" of a Unique Index in MySQL?

And how about the "cost" of a Primary Key/Index?

For example, I have a table with the following Fields and associated Indexes...

- id (PK)
- slug (Unique Index)
- name (Unique Index)
- created_on
- updated_on

I feel guilty having 3 Indexes of a Table with only 5 Fields, but what are you going to do?!