检查约束

--在性别列上添加check(检查约束)


--check约束语法
--alter table 表名
--add constraints 约束名 
--check(布尔表达式);
alter table students
add constraints ch_gender 
check(gender='男' or gender='女');


insert into students(stu_no, stu_name, gender, age)
values(3, 'lisi', '女', 23);


--在年龄列上添加check(年龄在1-120之间)
alter table students
add constraints ch_age
check(age > 0 and age <= 120);


insert into students(stu_no, stu_name, gender, age)
values(4, 'wangwu', '男', 23);


--在表中加入一个新的身份证号列
alter table students
add(id_card number(18));


--在年龄列上添加check(身份证号必须是18位)
alter table students
add constraints ch_id_card
check(length(id_card) = 18);


insert into students(stu_no, stu_name, gender, age, id_card)
values(5, 'wangwu', '男', 23, 430104198101012345);


insert into students(stu_no, stu_name, gender, age, id_card)
values(6, 'wangwu', '男', 23, 301041981010123456);