修改student表结构,添加约束,要求成绩grade不能低于0分,不能高于100分。
A.
alter table student add check(grade>=0 and grade<=100);
B.
alter table student add constraint student_grade_ck check(grade>=0 and grade<=100);
C.
alter table student add constraint student_grade_ck check(grade>=0 and <=100);
D.
alter table student add student_grade_ck check(grade>=0 and grade<=100);