mysql示例及练习2

#创建数据库并应用
create database shopdb;
use shopdb;

#创建表customers
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 decimal(12,2));

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

#在customers中添加数据
insert into customers values
(1,'Tom',25,'M','上海',10000),
(2,'Lucy',23,'F','广州',12000),
(3,'Jim',22,'M','北京',11000);

#在orders中添加数据
insert into orders values
(1,"iphone",5288),
(1,"ipad",3299),
(2,"iwatch",2222),
(2,"r11",4400);

1.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;

2.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%
select *,c_salary * 1.15 from customers where
c_age>=25 and c_city in ("北京","上海");
3、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="北京" order by c_salary limit 1;

4、选择工资c_salary最少的顾客的信息
select * from customers order by c_salary limit 1;

5、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 inner join customers on c_id = o_id;
(select c_id from customers where c_salary > 5000)
inner join orders on c_id = o_id;
6、删除外键限制

7、删除customers主键限制

8、增加customers主键限制c_id