CHAR() or VARCHAR() as primary key in an ISAM MySQL table?

Question

I need a simple table with a user name and password field in MySQL. Since user names must be unique, it makes sense to me to make them the primary key.

Is it better

Answer 1

I don't see CHAR used much in any MySQL databases i've worked on. I would go with the VARCHAR

For a CHAR(30) for example, the entire 30 characters are stored in the table meaning every entry will take up the same space, even if your username is only 10 characters long.

Using VARCHAR(30) it will only use enough space to store the string you have entered.

On a small table it wont make much difference, but on a larger table the VARCHAR should prove to keep it smaller overall.