Create mysql column with Key=MUL?

Question

I want to make a column with key = mul. What should I add to the following statement to make it do that?

alter table skills_required add column skill_id int (11) NOT NULL;

Thanks for the help!

Answer 1

Add a non-primary key on the field:

alter table skills_required add column skill_id int (11) NOT NULL
                          , add key ( skill_id )