1. -- 建表模板
    2. -- 外键表
    3. create table key_test
    4. (
    5.     id int auto_increment,
    6.     bh int not null unique,
    7.     constraint primary key pid(id desc )#指定使用倒序排列
    8. );
    9. drop table key_test;
    10. alter table key_test add name1 varchar(20) comment '名称';
    11. alter table key_test drop name1;
    12. alter table key_test alter column name1 varchar(20);#有些数据库无法使用
    13. select * from key_test order by id desc ;#倒序排列
    14. insert into key_test(bh) values (12),(13),(14),(15),(16),(17),(18),(19),(20),(21),(22);
    16. create table test_creat
    17. (
    18.     id      int,
    19.     for_key int comment '外键，参照表key_test',
    20.     name    varchar(20) unique not null comment '学生姓名',
    21.     age int comment '年龄' check (age>0 and age <100 ),
    22.     sex     char(2) check ( sex = '男' or sex= '女'),
    23.     address varchar(60) comment '家庭住址',
    24.     primary key pid(id),
    25.     foreign key fid(for_key) references key_test(id),
    26.     constraint id_check check ( id is not null)
    27. #     constraint primary key pt_id(id),
    28. #     constraint foreign key f_key(for_key) references key_test(id)
    29. );
    30. drop table test_creat;