【Day04-MySQL多表】

表间关系

项目开发中，因为业务之间相互关联，所以实体与实体之间存在联系，故而表跟表之间也存在着各种联系

我们把这种能够表示表间关系的数据库称为关系型数据库（RDBMS）,在数据库设计上，表关系分为三种：

• 一对多（多对一）

场景：班级和学生（一个班级对应多个学生，一个学生只能对应一个班级）

• 多对多

场景：学生和课程（一个学生对应多个课程，一个课程对应多个学生）

• 一对一

场景：丈夫和妻子（一个丈夫只有一个妻子，一个妻子也只有一个丈夫）

一对多

外键约束

外键分为物理外键和逻辑外键

1**、一对多的建表原则是什么****？**

在从表中添加一个外键列，指向主表的主键列

**2、**外键的作用是什么？

关联两张表，约束两张表的数据

3、什么是物理外键，什么是逻辑外键**？**

物理外键是使用foreign key实际定义的外键

逻辑外键是仅仅业务上的外键，没有实际约束力

多对多

1**、多对多的建表原则是什么****？**

新建一张中间表，作为两张主表的从表存在，

在中间表中创建两个外键，分别指向两张主表的主键

一对一

多表查询

交叉连接**(笛卡尔积)**

内连接

内连接2种写法的区别

1**、内连接查询到的是哪部分数据？**

完全符合两张表

2**、内连接格式是什么？**

左外连接

右外连接

1**、左外连接**

2**、右外连接**

子查询

案例：（多表查询）根据需求说明，设计合理的表结构

-- 分类表
create table category(
    id int unsigned primary key auto_increment comment '主键ID',
    name varchar(20) not null unique comment '分类名称',
    type tinyint unsigned not null comment '类型 1 菜品分类 2 套餐分类',
    sort tinyint unsigned not null comment '顺序',
    status tinyint unsigned not null default 0 comment '状态 0 禁用，1 启用',
    create_time datetime not null comment '创建时间',
    update_time datetime not null comment '更新时间'
) comment '分类' ;

-- 菜品表
create table dish(
    id int unsigned primary key auto_increment comment '主键ID',
    name varchar(20) not null unique comment '菜品名称',
    category_id int unsigned not null comment '菜品分类ID',
    price decimal(8, 2) not null comment '菜品价格',
    image varchar(300) not null comment '菜品图片',
    description varchar(200) comment '描述信息',
    status tinyint unsigned not null default 0 comment '状态, 0 停售 1 起售',
    create_time datetime not null comment '创建时间',
    update_time datetime not null comment '更新时间'
) comment '菜品';

-- 套餐表
create table setmeal(
    id int unsigned primary key auto_increment comment '主键ID',
    name varchar(20) not null unique comment '套餐名称',
    category_id int unsigned not null comment '分类id',
    price decimal(8, 2) not null comment '套餐价格',
    image varchar(300) not null comment '图片',
    description varchar(200) comment '描述信息',
    status tinyint unsigned not null default 0 comment '状态 0:停用 1:启用',
    create_time datetime not null comment '创建时间',
    update_time datetime not null comment '更新时间'
)comment '套餐' ;

-- 套餐菜品关联表
create table setmeal_dish(
    id int unsigned primary key auto_increment comment '主键ID',
    setmeal_id int unsigned not null comment '套餐id ',
    dish_id int unsigned not null comment '菜品id',
    copies tinyint unsigned not null comment '份数'
)comment '套餐菜品中间表';

-- ================================== 导入测试数据 ====================================
-- category
insert into category (id, type, name, sort, status, create_time, update_time) values (1, 1, '酒水饮料', 10, 1, '2022-08-09 22:09:18', '2022-08-09 22:09:18');
insert into category (id, type, name, sort, status, create_time, update_time) values (2, 1, '传统主食', 9, 1, '2022-08-09 22:09:32', '2022-08-09 22:18:53');
insert into category (id, type, name, sort, status, create_time, update_time) values (3, 2, '人气套餐', 12, 1, '2022-08-09 22:11:38', '2022-08-10 11:04:40');
insert into category (id, type, name, sort, status, create_time, update_time) values (4, 2, '商务套餐', 13, 1, '2022-08-09 22:14:10', '2022-08-10 11:04:48');
insert into category (id, type, name, sort, status, create_time, update_time) values (5, 1, '经典川菜', 6, 1, '2022-08-09 22:17:42', '2022-08-09 22:17:42');
insert into category (id, type, name, sort, status, create_time, update_time) values (6, 1, '新鲜时蔬', 7, 1, '2022-08-09 22:18:12', '2022-08-09 22:18:28');
insert into category (id, type, name, sort, status, create_time, update_time) values (7, 1, '汤类', 11, 1, '2022-08-10 10:51:47', '2022-08-10 10:51:47');

-- dish
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (1,'王老吉', 1, 6.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/41bfcacf-7ad4-4927-8b26-df366553a94c.png', '', 1, '2022-06-09 22:40:47', '2022-06-09 22:40:47');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (2,'北冰洋', 1, 4.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/4451d4be-89a2-4939-9c69-3a87151cb979.png', '还是小时候的味道', 1, '2022-06-10 09:18:49', '2022-06-10 09:18:49');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (3,'雪花啤酒', 1, 4.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/bf8cbfc1-04d2-40e8-9826-061ee41ab87c.png', '', 1, '2022-06-10 09:22:54', '2022-06-10 09:22:54');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (4,'米饭', 2, 2.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/76752350-2121-44d2-b477-10791c23a8ec.png', '精选五常大米', 1, '2022-06-10 09:30:17', '2022-06-10 09:30:17');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (5,'馒头', 2, 1.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/475cc599-8661-4899-8f9e-121dd8ef7d02.png', '优质面粉', 1, '2022-06-10 09:34:28', '2022-06-10 09:34:28');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (6,'老坛酸菜鱼', 5, 56.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/4a9cefba-6a74-467e-9fde-6e687ea725d7.png', '原料：汤，草鱼，酸菜', 1, '2022-06-10 09:40:51', '2022-06-10 09:40:51');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (7,'经典酸菜鮰鱼', 5, 66.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/5260ff39-986c-4a97-8850-2ec8c7583efc.png', '原料：酸菜，江团，鮰鱼', 1, '2022-06-10 09:46:02', '2022-06-10 09:46:02');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (8,'蜀味水煮草鱼', 5, 38.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/a6953d5a-4c18-4b30-9319-4926ee77261f.png', '原料：草鱼，汤', 1, '2022-06-10 09:48:37', '2022-06-10 09:48:37');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (9,'清炒小油菜', 6, 18.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/3613d38e-5614-41c2-90ed-ff175bf50716.png', '原料：小油菜', 1, '2022-06-10 09:51:46', '2022-06-10 09:51:46');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (10,'蒜蓉娃娃菜', 6, 18.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/4879ed66-3860-4b28-ba14-306ac025fdec.png', '原料：蒜，娃娃菜', 1, '2022-06-10 09:53:37', '2022-06-10 09:53:37');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (11,'清炒西兰花', 6, 18.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/e9ec4ba4-4b22-4fc8-9be0-4946e6aeb937.png', '原料：西兰花', 1, '2022-06-10 09:55:44', '2022-06-10 09:55:44');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (12,'炝炒圆白菜', 6, 18.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/22f59feb-0d44-430e-a6cd-6a49f27453ca.png', '原料：圆白菜', 1, '2022-06-10 09:58:35', '2022-06-10 09:58:35');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (13,'清蒸鲈鱼', 5, 98.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/c18b5c67-3b71-466c-a75a-e63c6449f21c.png', '原料：鲈鱼', 1, '2022-06-10 10:12:28', '2022-06-10 10:12:28');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (14,'东坡肘子', 5, 138.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/a80a4b8c-c93e-4f43-ac8a-856b0d5cc451.png', '原料：猪肘棒', 1, '2022-06-10 10:24:03', '2022-06-10 10:24:03');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (15,'梅菜扣肉', 5, 58.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/6080b118-e30a-4577-aab4-45042e3f88be.png', '原料：猪肉，梅菜', 1, '2022-06-10 10:26:03', '2022-06-10 10:26:03');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (16,'剁椒鱼头', 5, 66.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/13da832f-ef2c-484d-8370-5934a1045a06.png', '原料：鲢鱼，剁椒', 1, '2022-06-10 10:28:54', '2022-06-10 10:28:54');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (17,'馋嘴牛蛙', 5, 98.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/7a55b845-1f2b-41fa-9486-76d187ee9ee1.png', '配料：鲜活牛蛙，丝瓜，黄豆芽', 1, '2022-06-10 10:37:52', '2022-06-10 10:37:52');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (18,'鸡蛋汤', 7, 4.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/c09a0ee8-9d19-428d-81b9-746221824113.png', '配料：鸡蛋，紫菜', 1, '2022-06-10 10:54:25', '2022-06-10 10:54:25');
insert into dish (id, name, category_id, price, image, description, status, create_time, update_time) values (19,'平菇豆腐汤', 7, 6.00, 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/16d0a3d6-2253-4cfc-9b49-bf7bd9eb2ad2.png', '配料：豆腐，平菇', 1, '2022-06-10 10:55:02', '2022-06-10 10:55:02');

-- setmeal
insert into setmeal (id, category_id, name, price, status, description, image, create_time, update_time) values (1, 4, '商务套餐A', 20.00, 1, '', 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/21a5ed3a-97f6-447a-af9d-53deabfb5661.png', '2022-06-10 10:58:09', '2022-06-10 10:58:09');
insert into setmeal (id, category_id, name, price, status, description, image, create_time, update_time) values (2, 4, '商务套餐B', 22.00, 1, '', 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/8d0075f8-9008-4390-94ca-2ca631440304.png', '2022-06-10 11:00:13', '2022-06-10 11:11:37');
insert into setmeal (id, category_id, name, price, status, description, image, create_time, update_time) values (3, 3, '人气套餐A', 49.00, 1, '', 'https://reggie-itcast.oss-cn-beijing.aliyuncs.com/8979566b-0e17-462b-81d8-8dbace4138f4.png', '2022-06-10 11:11:23', '2022-06-10 11:11:23');

-- setmeal_dish
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (1, 1, 1, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (2, 1, 4, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (3, 1, 11, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (4, 2, 2, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (5, 2, 4, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (6, 2, 9, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (7, 3, 2, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (8, 3, 6, 1);
insert into setmeal_dish (id, setmeal_id, dish_id, copies) values (9, 3, 5, 1);

-- 1. 查询价格低于 10元 的菜品的名称、价格及其菜品的分类名称
select d.name,d.price,c.name
    from dish d
    join category c on d.category_id = c.id
    where d.price < 10;

-- 2. 查询所有价格在 10元(含)到50元(含)之间 且 状态为'起售'的菜品名称、价格 及其 菜品的分类名称 (即使菜品没有分类, 也需要将菜品查询出来).
select d.name,d.price,c.name
    from dish d
    left join category c on d.category_id = c.id
    where d.price between 10 and 50
    and d.status = 1;

-- 3. 查询出 "商务套餐A" 中包含了哪些菜品 （展示出套餐名称、价格, 包含的菜品名称、价格、份数）
select s.name,s.price,d.name,d.price,sd.copies
    from setmeal s
    join setmeal_dish sd on s.id = sd.setmeal_id
    join dish d on sd.dish_id = d.id
where s.name = '商务套餐A';

-- 4. 查询出低于菜品平均价格的菜品信息 (展示出菜品名称、菜品价格)
select name,price
    from dish
    where price < (select avg(price) from dish);


-- 5. 查询每个分类下最贵的菜品, 展示出分类的名称、最贵的菜品的价格
select c.name,max(price)
    from dish d
    join category c on c.id = d.category_id
    group by c.name;

-- 6. 查询各个分类下状态为'起售' , 并且该分类下菜品总数量大于等于3的分类名称
select c.name,count(1) as num
    from dish d
    join category c on c.id = d.category_id
    where d.status = 1
    group by c.name
    having num >= 3;

事务

事务介绍

一个业务操作包含多个子操作，如果这个业务操作被事务管理了，那么这些子操作要么同时成功，要么同时失败。

在MySQL数据库中，默认情况下，一条DML语句就是一个独立的事务。

SQL语法	描述
begin; (start transaction)	开启手动控制事务
commit;	提交事务
rollback;	回滚事务

-- 事务的三个api
-- 开启事务 begin;
-- 提交事务 commit;
-- 回滚事务 rollback;

begin; --开启事务
update account set money=money-10 where name = 'AA';
update account set money=money+10 where name = 'BB';
commit; -- 提交事务


begin; --开启事务
update account set money=money-10 where name = 'AA';
update account set money=money+10 where name = 'BB';
rollback; -- 回滚事务

事务特性

* 原子性：atomicity 事务是不可分割的最小单元，要么全部成功，要么全部失败

* 一致性：consistency 一个事务执行前后，数据库的状态是一致的

* 隔离性：isolation 当多个事务同时执行的时候，互相是不会产生影响的

* 持久性：durability 事务一旦提交或回滚，它对数据库中的数据的改变就是永久的

事务隔离性带来的问题

* 脏读：一个事务读取到了另外一个事务没有提交的数据

* 不可重复读：一个事务读取到了另外一个事务修改的数据（修改）

* 幻读（虚读）：一个事务读取到了另外一个事务新增的数据（新增）

事务隔离级别

级别	名字	隔离级别	脏读	不可重复读	幻读	数据库默认隔离级别
1	读未提交	read uncommitted	是	是	是
2	读已提交	read committed	否	是	是	Oracle
3	可重复读	repeatable read	否	否	是	MySQL
4	串行化	serializable	否	否	否