MySQL基础操作案例

综述：两张表，一张顾客信息表customers，一张订单表orders

创建一张顾客信息表customers，字段要求如下：
c_id 类型为整型，设置为主键，并设置为自增长属性
c_name 字符类型，变长，宽度为20
c_age 微小整型，取值范围为0~255(无符号)
c_sex 枚举类型，要求只能在('M','F')中选择一个值
c_city 字符类型，变长，宽度为20
c_salary 浮点类型，要求整数部分最大为10位，小数部分为2位

    create table customers(
    c_id int primary key auto_increment,
    c_name varchar(20),
    c_age tinyint unsigned,
    c_sex enum("M","F"),
    c_city varchar(20),
    c_salary float(12,2)
    );

在表中任意插入3条记录,c_name为"Zhangsan","Lisi","Wangwu", c_city尽量写"Beijing","Shanghai" ......

    insert into customers values
    (1,"Zhangsan",25,"M","Beijing",8000),
    (2,"Lisi",30,"F","Shanghai",10000),
    (3,"Wangwu",27,"M","Shenzhen",3000);

创建一张订单表orders，字段要求如下：

o_id 整型
o_name 字符类型，变长，宽度为30
o_price 浮点类型，整数最大为10位，小数部分为2位
设置此表中的o_id字段为customers表中c_id字段的外键,更新删除同步

    create table orders(
    o_id int,
    o_name varchar(30),
    o_price float(12,2),
    foreign key(o_id) references customers(c_id)
    on delete cascade
    on update cascade
    );

在表中任意插入5条记录(注意外键限制)

o_name分别为"iphone","ipad","iwatch","mate9","r11",其他信息自己定

    insert into orders values
    (1,"iphone",5288),
    (1,"ipad",3299),
    (3,"mate9",3688),
    (2,"iwatch",2222),
    (2,"r11",4400);

返回customers表中，工资大于4000元，或者年龄小于29岁，满足这样条件的前2条记录

  select * from customers where c_salary > 4000 or c_age < 29 limit 2;

把customers表中，年龄大于等于25岁，并且地址是北京或者上海，这样的人的工资上调15%

  update customers set c_salary=c_salary*1.15 where c_age >= 25 and c_city in ("Beijing","Shanghai");

把customers表中，城市为北京的顾客，按照工资降序排列，并且只返回结果中的第一条记录

  select * from customers where c_city="Beijing" order by c_salary desc limit 1;

选择工资c_salary最少的顾客的信息

  select * from customers 
  where c_salary = (select min(c_salary) from customers);

找到工资大于5000的顾客都买过哪些产品的记录明细

  select * from orders where o_id in (select c_id from customers where c_salary > 5000);

删除外键限制

  1、show create table orders;
  2、alter table orders drop foreign key orders_ibfk_1;

删除customers主键限制

  1、删除自增长属性
    alter table customers modify c_id int;
  2、删除主键限制
    alter table customers drop primary key;

增加customers主键限制c_id

  alter table customers add primary key(c_id);