JavaWeb - Day08 - MySQL - 多表查询、事务、索引 - Mybatis - 入门

#建议：创建新的数据库
create database db04;
use db04;

-- 部门表
create table tb_dept
(
    id          int unsigned primary key auto_increment comment '主键ID',
    name        varchar(10) not null unique comment '部门名称',
    create_time datetime    not null comment '创建时间',
    update_time datetime    not null comment '修改时间'
) comment '部门表';
-- 部门表测试
insert into tb_dept (id, name, create_time, update_time)
values (1, '学工部', now(), now()),
       (2, '教研部', now(), now()),
       (3, '咨询部', now(), now()),
       (4, '就业部', now(), now()),
       (5, '人事部', now(), now());

-- 员工表
create table tb_emp
(
    id          int unsigned primary key auto_increment comment 'ID',
    username    varchar(20)      not null unique comment '用户名',
    password    varchar(32) default '123456' comment '密码',
    name        varchar(10)      not null comment '姓名',
    gender      tinyint unsigned not null comment '性别, 说明: 1 男, 2 女',
    image       varchar(300) comment '图像',
    job         tinyint unsigned comment '职位, 说明: 1 班主任,2 讲师, 3 学工主管, 4 教研主管, 5 咨询师',
    entrydate   date comment '入职时间',
    dept_id     int unsigned comment '部门ID',
    create_time datetime         not null comment '创建时间',
    update_time datetime         not null comment '修改时间'
) comment '员工表';
-- 员工表测试数据
INSERT INTO tb_emp(id, username, password, name, gender, image, job, entrydate,dept_id, create_time, update_time) 
VALUES 
(1,'jinyong','123456','金庸',1,'1.jpg',4,'2000-01-01',2,now(),now()),
(2,'zhangwuji','123456','张无忌',1,'2.jpg',2,'2015-01-01',2,now(),now()),
(3,'yangxiao','123456','杨逍',1,'3.jpg',2,'2008-05-01',2,now(),now()),
(4,'weiyixiao','123456','韦一笑',1,'4.jpg',2,'2007-01-01',2,now(),now()),
(5,'changyuchun','123456','常遇春',1,'5.jpg',2,'2012-12-05',2,now(),now()),
(6,'xiaozhao','123456','小昭',2,'6.jpg',3,'2013-09-05',1,now(),now()),
(7,'jixiaofu','123456','纪晓芙',2,'7.jpg',1,'2005-08-01',1,now(),now()),
(8,'zhouzhiruo','123456','周芷若',2,'8.jpg',1,'2014-11-09',1,now(),now()),
(9,'dingminjun','123456','丁敏君',2,'9.jpg',1,'2011-03-11',1,now(),now()),
(10,'zhaomin','123456','赵敏',2,'10.jpg',1,'2013-09-05',1,now(),now()),
(11,'luzhangke','123456','鹿杖客',1,'11.jpg',5,'2007-02-01',3,now(),now()),
(12,'hebiweng','123456','鹤笔翁',1,'12.jpg',5,'2008-08-18',3,now(),now()),
(13,'fangdongbai','123456','方东白',1,'13.jpg',5,'2012-11-01',3,now(),now()),
(14,'zhangsanfeng','123456','张三丰',1,'14.jpg',2,'2002-08-01',2,now(),now()),
(15,'yulianzhou','123456','俞莲舟',1,'15.jpg',2,'2011-05-01',2,now(),now()),
(16,'songyuanqiao','123456','宋远桥',1,'16.jpg',2,'2007-01-01',2,now(),now()),
(17,'chenyouliang','123456','陈友谅',1,'17.jpg',NULL,'2015-03-21',NULL,now(),now());

select * from  tb_emp , tb_dept;

select * from tb_emp , tb_dept where tb_emp.dept_id = tb_dept.id ;

select  字段列表   from   表1 , 表2   where  条件 ... ;

select  字段列表   from   表1  [ inner ]  join 表2  on  连接条件 ... ;

select tb_emp.name , tb_dept.name -- 分别查询两张表中的数据
from tb_emp , tb_dept -- 关联两张表
where tb_emp.dept_id = tb_dept.id; -- 消除笛卡尔积

select tb_emp.name , tb_dept.name
from tb_emp inner join tb_dept
on tb_emp.dept_id = tb_dept.id;

select emp.name , dept.name
from tb_emp emp inner join tb_dept dept
on emp.dept_id = dept.id;

select  字段列表   from   表1  left  [ outer ]  join 表2  on  连接条件 ... ;

select  字段列表   from   表1  right  [ outer ]  join 表2  on  连接条件 ... ;

-- 左外连接：以left join关键字左边的表为主表，查询主表中所有数据，以及和主表匹配的右边表中的数据
select emp.name , dept.name
from tb_emp AS emp left join tb_dept AS dept 
     on emp.dept_id = dept.id;

-- 右外连接
select dept.name , emp.name
from tb_emp AS emp right join  tb_dept AS dept
     on emp.dept_id = dept.id;

SELECT  *  FROM   t1   WHERE  column1 =  ( SELECT  column1  FROM  t2 ... );

-- 1.查询"教研部"部门ID
select id from tb_dept where name = '教研部';    #查询结果：2
-- 2.根据"教研部"部门ID, 查询员工信息
select * from tb_emp where dept_id = 2;

-- 合并出上两条SQL语句
select * from tb_emp where dept_id = (select id from tb_dept where name = '教研部');

-- 1.查询"方东白"的入职日期
select entrydate from tb_emp where name = '方东白';     #查询结果：2012-11-01
-- 2.查询指定入职日期之后入职的员工信息
select * from tb_emp where entrydate > '2012-11-01';

-- 合并以上两条SQL语句
select * from tb_emp where entrydate > (select entrydate from tb_emp where name = '方东白');

-- 1.查询"销售部"和"市场部"的部门ID
select id from tb_dept where name = '教研部' or name = '咨询部';    #查询结果：3,2
-- 2.根据部门ID, 查询员工信息
select * from tb_emp where dept_id in (3,2);

-- 合并以上两条SQL语句
select * from tb_emp where dept_id in (select id from tb_dept where name = '教研部' or name = '咨询部');

-- 查询"韦一笑"的入职日期 及 职位
select entrydate , job from tb_emp where name = '韦一笑';  #查询结果： 2007-01-01 , 2
-- 查询与"韦一笑"的入职日期及职位相同的员工信息
select * from tb_emp where (entrydate,job) = ('2007-01-01',2);

-- 合并以上两条SQL语句
select * from tb_emp where (entrydate,job) = (select entrydate , job from tb_emp where name = '韦一笑');

select * from emp where entrydate > '2006-01-01';

select e.*, d.* from (select * from emp where entrydate > '2006-01-01') e left join dept d on e.dept_id = d.id ;

/*查询技巧：
     明确1：查询需要用到哪些字段
        菜品名称、菜品价格 、 菜品分类名
     明确2：查询的字段分别归属于哪张表
        菜品表：[菜品名称、菜品价格]
        分类表：[分类名]
     明确3：如查多表，建立表与表之间的关联
        菜品表.caategory_id = 分类表.id
     其他：（其他条件、其他要求）
        价格 < 10
*/
select d.name , d.price , c.name
from dish AS d , category AS c
where d.category_id = c.id
      and d.price < 10;

select d.name , d.price, c.name
from dish AS d left join category AS c on d.category_id = c.id
where d.price between 10 and 50
      and d.status = 1;

select c.name , max(d.price)
from dish AS d , category AS c
where d.category_id = c.id
group by c.name;

/*查询技巧：
     明确1：查询需要用到哪些字段
        分类名称、菜品总数量
     明确2：查询用到的字段分别归属于哪张表
        分类表：[分类名]
        菜品表：[菜品状态]
     明确3：如查多表，建立表与表之间的关联
        菜品表.caategory_id = 分类表.id
     其他：（其他条件、其他要求）
        条件：菜品状态 = 1 (1表示起售)
        分组：分类名
        分组后条件： 总数量 >= 3
*/
select c.name , count(*)
from dish AS d , category AS c
where d.category_id = c.id
      and d.status = 1 -- 起售状态
group by c.name  -- 按照分类名分组
having count(*)>=3; -- 各组后筛选菜品总数据>=3

select s.name, s.price, d.name, d.price, sd.copies
from setmeal AS s , setmeal_dish AS sd , dish AS d
where s.id = sd.setmeal_id and sd.dish_id = d.id
      and s.name='商务套餐A';

-- 1.计算菜品平均价格
select avg(price) from dish;    -- 查询结果：37.736842
-- 2.查询出低于菜品平均价格的菜品信息
select * from dish where price < 37.736842;

-- 合并以上两条SQL语句
select * from dish where price < (select avg(price) from dish);

-- 删除学工部
delete from dept where id = 1;  -- 删除成功

-- 删除学工部的员工
delete from emp where dept_id = 1; -- 删除失败（操作过程中出现错误：造成删除没有成功）

-- 开启事务
start transaction ;

-- 删除学工部
delete from tb_dept where id = 1;

-- 删除学工部的员工
delete from tb_emp where dept_id = 1;

-- 提交事务 (成功时执行)
commit ;

-- 回滚事务 (出错时执行)
rollback ;

-- 添加索引
create index idx_sku_sn on tb_sku (sn);  #在添加索引时，也需要消耗时间

-- 查询数据（使用了索引）
select * from tb_sku where sn = '100000003145008';

create  [ unique ]  index 索引名 on  表名 (字段名,... ) ;

create index idx_emp_name on tb_emp(name);

show  index  from  表名;

show  index  from  tb_emp;

drop  index  索引名  on  表名;

drop index idx_emp_name on tb_emp;

<!-- 仅供参考：只粘贴了pom.xml中部分内容 -->
<dependencies>
        <!-- mybatis起步依赖 -->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.3.0</version>
        </dependency>

        <!-- mysql驱动包依赖 -->
        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </dependency>
        
        <!-- spring单元测试 (集成了junit) -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
</dependencies>

-- 用户表
create table user(
    id int unsigned primary key auto_increment comment 'ID',
    name varchar(100) comment '姓名',
    age tinyint unsigned comment '年龄',
    gender tinyint unsigned comment '性别, 1:男, 2:女',
    phone varchar(11) comment '手机号'
) comment '用户表';

-- 测试数据
insert into user(id, name, age, gender, phone) VALUES (null,'白眉鹰王',55,'1','18800000000');
insert into user(id, name, age, gender, phone) VALUES (null,'金毛狮王',45,'1','18800000001');
insert into user(id, name, age, gender, phone) VALUES (null,'青翼蝠王',38,'1','18800000002');
insert into user(id, name, age, gender, phone) VALUES (null,'紫衫龙王',42,'2','18800000003');
insert into user(id, name, age, gender, phone) VALUES (null,'光明左使',37,'1','18800000004');
insert into user(id, name, age, gender, phone) VALUES (null,'光明右使',48,'1','18800000005');

public class User {
    private Integer id;   //id（主键）
    private String name;  //姓名
    private Short age;    //年龄
    private Short gender; //性别
    private String phone; //手机号
    
    //省略GET, SET方法
}

#驱动类名称
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
#数据库连接的url
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis
#连接数据库的用户名
spring.datasource.username=root
#连接数据库的密码
spring.datasource.password=1234

import com.itheima.pojo.User;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;
import java.util.List;

@Mapper
public interface UserMapper {
    
    //查询所有用户数据
    @Select("select id, name, age, gender, phone from user")
    public List<User> list();
    
}

@SpringBootTest
public class MybatisQuickstartApplicationTests {
    
    @Autowired
    private UserMapper userMapper;
    
    @Test
    public void testList(){
        List<User> userList = userMapper.list();
        for (User user : userList) {
            System.out.println(user);
        }
    }

}

import com.itheima.pojo.User;
import org.junit.jupiter.api.Test;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class JdbcTest {
    @Test
    public void testJdbc() throws Exception {
        //1. 注册驱动
        Class.forName("com.mysql.cj.jdbc.Driver");

        //2. 获取数据库连接
        String url="jdbc:mysql://127.0.0.1:3306/mybatis";
        String username = "root";
        String password = "1234";
        Connection connection = DriverManager.getConnection(url, username, password);

        //3. 执行SQL
        Statement statement = connection.createStatement(); //操作SQL的对象
        String sql="select id,name,age,gender,phone from user";
        ResultSet rs = statement.executeQuery(sql);//SQL查询结果会封装在ResultSet对象中

        List<User> userList = new ArrayList<>();//集合对象（用于存储User对象）
        //4. 处理SQL执行结果
        while (rs.next()){
            //取出一行记录中id、name、age、gender、phone下的数据
            int id = rs.getInt("id");
            String name = rs.getString("name");
            short age = rs.getShort("age");
            short gender = rs.getShort("gender");
            String phone = rs.getString("phone");
            //把一行记录中的数据，封装到User对象中
            User user = new User(id,name,age,gender,phone);
            userList.add(user);//User对象添加到集合
        }
        //5. 释放资源
        statement.close();
        connection.close();
        rs.close();

        //遍历集合
        for (User user : userList) {
            System.out.println(user);
        }
    }
}

#驱动类名称
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
#数据库连接的url
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis
#连接数据库的用户名
spring.datasource.username=root
#连接数据库的密码
spring.datasource.password=1234

@Mapper
public interface UserMapper {
    @Select("select id, name, age, gender, phone from user")
    public List<User> list();
}

<dependency>
   <groupId>com.alibaba</groupId>
   <artifactId>druid-spring-boot-starter</artifactId>
   <version>1.2.8</version>
</dependency>

spring.datasource.druid.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.druid.url=jdbc:mysql://localhost:3306/mybatis
spring.datasource.druid.username=root
spring.datasource.druid.password=1234

spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis
spring.datasource.username=root
spring.datasource.password=1234

<!-- 在springboot的父工程中，已经集成了lombok并指定了版本号，故当前引入依赖时不需要指定version -->
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
</dependency>

import lombok.Data;

@Data
public class User {
    private Integer id;
    private String name;
    private Short age;
    private Short gender;
    private String phone;
}

import lombok.Data;

@Data //getter方法、setter方法、toString方法、hashCode方法、equals方法
@NoArgsConstructor //无参构造
@AllArgsConstructor//全参构造
public class User {
    private Integer id;
    private String name;
    private Short age;
    private Short gender;
    private String phone;
}