Mysql - Make combination of two columns unique

Question

i have a mysql database table with two columns of importance, the university_id column and username column. Here the university_id should be unique to the whole table, but the two columns can repeat many times but the same combinations must not repeat, the username should be unique only to the university_id. here is what i mean

 id   university_id     username
 1       10001           DrDre
 2       10002          slimshady
 3       10003          slimshady
 4       10004           DrDre
 5       10005           lilwyn
 6       10005           lilwyn <- only this line would be illegal 
 7       10005          kanyeEast

• if possible i would also like to know how to do it using doctrine in symfony2

-thanks

Answer 1

use below alter statement if you did not make any constraint on table-

alter table mytable 
add unique key Uk_university_id(university_id), 
add unique key Uk_unvid_username(university_id,username);

Update:

alter table mytable  
add unique key Uk_unvid_username(university_id,username);