Adding constraint to an existing table column I have a table that doesnt have any constraint on them like this 

CREATE TABLE SomeTable
(
   Id int NOT NULL,
   Type varchar(50),
)

insert into SomeTable values (12,'Exchange-Student');


Now I know that I can do alter into add constraint and then check if type is of my desired value.
I just dont know how to implement it correctly. 

For example lets say that I want it to be restricted to 3 types 'Exchange-Studen', 'Independent student' and 'program Student'

How would I implement that ?
To alter ypour existing table use

ALTER TABLE SomeTable 
ADD CONSTRAINT `Student_type2` CHECK (Type IN 
('Exchange-Student','Independent student','program Student'))


Or ad following to the CREATE TABLE seperated by comma

CONSTRAINT `Student_type2` CHECK (Type IN 
('Exchange-Student','Independent student','program Student')