准备数据
1>创建数据表
创建丝芙兰数据库
create database SEPHORE charset=utf8;
创建一个商品goods数据表
create table goods(
id int unsigned primary key auto_increment not null,
name varchar(150) not null, -- 商品名称
cate_name varchar(40) not null, -- 商品类别
brand_name varchar(40) not null, -- 品牌
price decimal(10,3) not null default 0,-- 价格
is_show bit not null default 1, -- 默认显示 显示不显示
is_saleoff bit not null default 0
)
2>插入数据
在 goods商品表插入商品
insert into goods values
(0,'SK-II护肤精华露“神仙水SK-II
FACIAL TREATMENT ESSENCE VALUE SET”+大眼眼霜惠选套组',
'神仙水+眼霜','SK-II','2130',default,default);
要插入多个数据 这里只列出一个
2 SQL语句演练
1 查询类型cate_name为 '口红' 的商品名称、价格
select * from goods where cate_name = '口红';
select name as 商品名称,price as 商品价格 from goods where cate_name = '口红';
2 显示商品种类
select distinct cate_name from goods; 去重
select cate_name from goods group by cate_name; 分组效率低 数据复杂建议用
3 查每个种类的商品名称
select cate_name,group_concat(name) from goods group by cate_name;
4 删除goods表
drop table goods;
5 查询类型cate_name为 '眼霜' 的商品名称、价格
select name,price from goods where cate_name = '眼霜';
6 显示商品的种类
select cate_name from goods group by cate_name;
7 求所有产品的平均价格,并且保留两位小数
select round(avg(price),2) from goods;
8 显示每种商品的平均价格
select cate_name from goods group by cate_name; -- 商品种类
select cate_name,avg(price) from goods group by cate_name;
9 查询每种类型的商品中 最贵、最便宜、平均价、数量
select cate_name,max(price),min(price),avg(price),count(*) from goods group by cate_name;
10 查询所有价格大于平均价格的商品，并且按价格降序排序
select avg(price) from goods;
select * from goods where price>987.2;
-- 创建商品分类表
create table if not exists goods_cates(
id int unsigned primary key auto_increment,
name varchar(40) not null
);
-- 创建商品品牌表
create table if not exists goods_brands(
id int unsigned primary key auto_increment,
name varchar(40) not null
);
-- 查询goods表中商品的种类
select cate_name from goods group by cate_name;
-- 查询goods表中商品的品牌
select brand_name from goods group by brand_name;
-- 将分组结果写入到goods_cates数据表
insert into goods_cates (name) select cate_name from
goods group by cate_name;
-- 将分组结果写入到goods_brands数据表
insert into goods_brands (name) select brand_name from
goods group by brand_name;
-- 通过goods_cates数据表来更新goods表
update goods as g inner join goods_cates as c on
g.cate_name=c.name set g.cate_name=c.id;
-- 通过goods_cates数据表来更新goods表
update goods as g inner join goods_brands as b on
g.brand_name=b.name set g.brand_name=b.id;
-- 分别在 goods_cates 和 goods_brands表中插入记录
insert into goods_cates(name) values (
'路由器'),('交换机'),('网卡');
insert into goods_brands(name) values
('海尔'),('清华同方'),('神舟');
-- 在 goods 数据表中写入任意记录
insert into goods (name,cate_name,brand_name,price)
values('LaserJet Pro P1606dn 黑白激光打印机', 12, 4,'1849');
-- 查询所有商品的详细信息 (通过内连接)
select g.id,g.name,c.name,b.name,g.price from goods as g
inner join goods_cates as c on g.cate_id=c.id
inner join goods_brands as b on g.brand_id=b.id;
-- 查询所有商品的详细信息 (通过左连接)
select g.id,g.name,c.name,b.name,g.price from goods as g
left join goods_cates as c on g.cate_id=c.id
left join goods_brands as b on g.brand_id=b.id;
-- 如何防止无效信息的插入,就是可以在插入前判断类型或者品牌名称是否存在呢? 可以使用之前讲过的外键来解决
-- 外键约束:对数据的有效性进行验证
-- 关键字: foreign key,只有 innodb数据库引擎 支持外键约束
对于已经存在的数据表 如何更新外键约束
-- 给brand_id 添加外键约束成功
alter table goods add foreign key (brand_id)
references goods_brands(id);
-- 给cate_id 添加外键约束成功
alter table goods add foreign key (cate_id)
references goods_cates(id);
-- 给cate_id 添加外键失败
-- 会出现1452错误
-- 错误原因:已经添加了一个不存在的cate_id值12,因此需要先删除
alter table goods add foreign key (cate_id) references
goods_cates(id);
insert into goods_brands (name) select brand_name from
goods group by brand_name;
select brand_name from goods group by brand_name;
insert into goods_cates (name) select cate_name from
goods group by cate_name;
Query OK, 15 rows affected (0.03 sec)
Records: 15 Duplicates: 0 Warnings: 0
update goods as g inner join goods_cates as c on
g.cate_name=c.name set g.cate_name=c.id;
update goods Type='int(10) unsigned' where Field='cate_name';
修改表结构
这是改类别表的，把名字cate_name 换成cate_id，类型是 int unsigned
alter table goods
change cate_name cate_id int unsigned not null;
alter table goods
change brand_name brand_id int unsigned not null;
取消外键
alter table goods drop foreign key goods_ibfk_1;
alter table goods drop foreign key goods_ibfk_2;