1、數據庫操作
create database db_name; 建庫
drop database db_name; 刪庫
2、建立數據表
先選擇數據庫
use db_name;
create table `table_name`(
order_id int(10) not null auto_increment primary key,
)engine=myisam default charset=utf8;
3、數據表操作
rename table`old_table_name` to`new_table_name`;
alter table `table_name` change column old_column_name new_column_name int(10) not null;
4、表數據操作
添
insert into `order` (uid,procuct_id) values(2,4),(2,3),(2,7);
insert into `order` (order_id,uid,product_id) values(0,4,4),(null,4,3);
insert into `order` values(0,3,4);
insert into `order` values(null,3,5);
insert into `order` set uid=4,product_id=4;
刪
delete from `order` where order_id=12;
delete from `order`;
改
update `order` set product_id=2 where uid=1;
查
select
* from `order` where uid=1 group by product_id having product_id>2 order by order_id desc;
5、經典題型
create table `user`(
uid int(10) not null auto_increment primary key,
username varchar(20) not null,
passwd varchar(20) not null
)engine=myisam default charset=utf8;
create table `order`(
order_id int(10) not null auto_increment primary key,
)engine=myisam default charset=utf8;
(1)查詢訂單最多的用戶名 select user.username from user left
join (select uid,count(*) as c from `order` group by uid
order by c desc) as O on user.uid=O.uid limit 1;
select user.username from user right join (select uid,count(*) as c from `order` group by uid
order by c desc limit 1) as O on user.uid=O.uid;
select user.username from (select uid,count(*) as c from `order` group by uid order by c desc limit 1)
as O left join user on user.uid=O.uid;
select username from user where uid=(select uid from `order` group by uid order by count(*) desc limit 1)
(2)查詢沒有下訂單的用戶
select username from user where uid not in (select distinct uid from `order`);