Cost of Single Primary Key VS Multiple Primary Key

[Paul Y]

Hi everyone,

Could someone advise me on difference between the cost of using a single primary key and multiple primary key? Especially on their effect on joins?

For example, with the following table

---+-----+-------+-----
ID | Name| Class | Test
---+-----+-------+-----

is it more cost effective to use a single unique primary key (ID) or use a multiple primary key pair (Name + Class + Test)

Thank you for your help!