m not really sure but i think candidate key is the column which qualifies to be a primary key.
so u can set this column as primary key if u wish to at a later date.
but i dont think you can assign a candidate key
But Sir, I don't want to set the key as primary key..
Actually, I am sorry not to tell my problem in detail..
Specifically, I have a table with enrolno as primary key and I want to make classid As Candidate key, because I want to reference ClassID from a foreign key of another table. For that when I use the query to set FOREIGN KEY constraint that refers to the classid of this table,i get the error asking for classid to be either primary or candidate key..