sql 复习

创建表

#设置外键
create table example3(id int primary key,
    stu_id int,
    course_id int,
    constraint c_fk foreign key(stu_id,course_id) 
    references example2(stu_id,course_id));
# not null
create table example4(id int not null primary key,
    name varchar(20) not null,
    stu_id int,
    constraint d_fk foreign key(stu_id)
    references example1(stu_id));
#..
create table example5(id int primary key,
    stu_id int unique,
    name varchar(20) not null);
#..
create table example6(id int primary key auto_increment,
    stu_id int unique,
    name varchar(20) not null);
#..
create table example7(id int primary key auto_increment,
    stu_id int unique,
    name varchar(20) not null,
    english varchar(20) default 'zero',
    math float default 0,
    computer float default 0);

修改表

#alter table;
alter table example0 rename user;

alter table user modify name varchar(30);

alter table user change id stu_id int;

alter table user add age int(4) not null;

alter table user add num int(8) primary key first;