九：SQL之DQL数据查询语言多表操作

Posted 2020-12-02 wdmlsx

前言：

一：数据准备

　　员工表emp 和部门表 dept

--分别创建部门和员工表，并实现一对多关系
DROP TABLE dept;
CREATE TABLE `dept`(
    `d_id` INT(5) PRIMARY KEY AUTO_INCREMENT COMMENT ‘这是部门id主键自增长‘,
    `d_name` VARCHAR(30) NOT NULL UNIQUE COMMENT ‘这是部门名称唯一非空‘    
);

CREATE TABLE `emp`(
    `e_id` INT PRIMARY KEY AUTO_INCREMENT COMMENT ‘这是员工表的主键自增长‘,
    `e_uname` VARCHAR(10)  NOT NULL UNIQUE COMMENT ‘这是登录名‘,
    `e_name` VARCHAR(20) NOT NULL COMMENT ‘这是真实姓名‘,
    `e_pwd` VARCHAR(20) DEFAULT ‘123456‘ COMMENT ‘这是密码默认为123456‘,
    `e_d_id` INT(5),
    CONSTRAINT `emp_fk` FOREIGN KEY (`e_d_id`) REFERENCES dept (`d_id`)
);

--准备数据
--先给dept录入测试数据
INSERT INTO dept VALUES(NULL,‘财务部‘),(NULL,‘技术部‘),(NULL,‘营销部‘),(NULL,‘采购部‘),(NULL,‘市场部‘);
INSERT INTO dept VALUES(NULL,‘行政部‘),(NULL,‘后勤部‘),(NULL,‘总经办‘),(NULL,‘人事部‘),(NULL,‘策划部‘);
--给emp录入测试数据
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘lqd‘,‘刘强东‘,20);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘mht‘,‘马化腾‘,17);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘my‘,‘马云‘,8);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘lyf‘,‘刘亦菲‘,16);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘wjl‘,‘王健林‘,9);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zzt‘,‘章泽天‘,17);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘ldh‘,‘刘德华‘,10);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘dl‘,‘丁磊‘,16);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zhy‘,‘周鸿祎‘,18);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zzy‘,‘章子怡‘,9);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘abm‘,‘奥巴马‘,19);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zjl‘,‘周杰伦‘,7);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zcy‘,‘张朝阳‘,16);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zj‘,‘周洁‘,19);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘syp‘,‘苏有朋‘,20);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘fxg‘,‘冯小刚‘,20);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘wsc‘,‘王思聪‘,10);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘hxn‘,‘韩晓诺‘,19);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘zy‘,‘曾洋‘,7);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘hh‘,‘韩寒‘,6);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘mbp‘,‘姆巴佩‘,17);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘gjm‘,‘郭敬明‘,7);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘wsc‘,‘王宝强‘,10);
INSERT INTO emp (e_uname,e_name,e_d_id)VALUES(‘xjy‘,‘许家印‘,6);

准备数据dept和emp

二：