Question

I have table that doesn’t need a specific field to be the primary key. I could add a auto-increment ID field, but it won’t be used at all within database queries…

Can I make a UNIQUE KEY to be primary too?

the UNIQUE KEY consists of two fields paired together:

a VARCHAR(64) NOT NULL,
b VARCHAR(64) NOT NULL,
UNIQUE KEY uk_ab(a,b)

Answer 1

Sure (no need for UNIQUE KEY):

PRIMARY KEY (a, b)

Have a look at the documentation:

A PRIMARY KEY is a unique index where all key columns must be defined as NOT NULL. If they are not explicitly declared as NOT NULL, MySQL declares them so implicitly (and silently). A table can have only one PRIMARY KEY. The name of a PRIMARY KEY is always PRIMARY, which thus cannot be used as the name for any other kind of index.

and

A PRIMARY KEY can be a multiple-column index. However, you cannot create a multiple-column index using the PRIMARY KEY key attribute in a column specification. Doing so only marks that single column as primary. You must use a separate PRIMARY KEY(index_col_name, ...) clause.