The following syntax is used to add check to the table at the time of its creation.
CREATE TABLE (col datatype, check(condition), col2 datatype,...)
More than one check constraints can be added to a single table. This will put a limitation to the values of an specific domain.
create table student(name char(20), age int check(age<=20))
The above code will add a constraint to the student table at the time of its creation to restrict the age value to 20.