前言
最近复习了下Mysql，感觉写好SQL语句不是一件容易的事，还是要多进行练习才能写好SQL语句 于是在网上看了视频，跟着写了下来~ 流程和思路都写在源码中
练习
表的结构
表的内容
emp表
dept表
salarygrade表
job表
源码
-- 多表查询练习 -- 部门表 create TABLE dept ( id INT PRIMARY KEY, dname VARCHAR(255), loc VARCHAR(255) ); -- 添加四个部门 INSERT INTO dept VALUES (10,"教研部","北京"), (20,"学工部","上海"), (30,"销售部","广州"), (40,"财务部","深圳"); -- 职务表 CREATE TABLE job ( id INT PRIMARY KEY, jname VARCHAR(25), description VARCHAR(90) ) -- 添加4个职务 INSERT INTO job (id,jname,description) VALUES (1,"董事长","管理公司，接单"), (2,"经理","管理部门员工"), (3,"销售员","向客人推销产品"), (4,"文员","使用office") --员工表 CREATE TABLE emp ( id INT PRIMARY KEY, -- 员工id ename VARCHAR (50), -- 员工姓名 job_id INT, -- 职务id mgr INT, -- 上级领导 joindate DATE, -- 入职日期 salary DECIMAL(7,2), -- 工资 bonus DECIMAL (7,2),-- 奖金 dept_id INT, -- 所在部门编号 CONSTRAINT emp_jobid_ref_job_id_fk FOREIGN KEY (job_id) REFERENCES job(id), CONSTRAINT emp_deptid_ref_dept_id_fk FOREIGN KEY(dept_id) REFERENCES dept(id) ); -- 添加员工 INSERT INTO emp(id,ename,job_id,mgr,joindate,salary,bonus,dept_id) VALUES (1001,"孙悟空",4,1004,'2000-12-17',8000.00,NULL,20), (1002,"卢俊义",3,1006,'2001-02-20',16000.00,3000.00,30), (100,"林冲",3,1006,'2001-02-22',12500.00,5000.00,30), (1004,"唐僧",2,1009,'2001-04-02',29750.00,NULL,20), (1005,"李逵",4,1006,'2001-09-28',12500.00,14000.00,30), (1006,"宋江",2,1009, '2001-05-01',28500.00,NULL,30), (1007,"刘备",2,1009,'2001-09-01',24500.00,NULL,10), (1008,"猪八戒",4,1004,'2007-04-19',30000.00,NULL,20), (1009,"罗贯中",1,NULL,'2001-11-17',50000.00,NULL,10), (1010,"吴用",3,1006,'2001-09-08',15000.00,0.00,30), (1011,"沙僧",4,1004,'2007-05-23',11000.00,NULL,20), (1012,"李逵",4,1006,'2001-12-03',9500.00,NULL,30), (1013,"小白龙",4,1004,'2001-12-03',30000.00,NULL,20), (1014,"关羽",4,1007,'2002-01-23',13000.00,NULL,10); -- 工资等级表 CREATE TABLE salarygrade ( grade int PRIMARY KEY, losalary INT, hisalary INT ); -- 添加5个工资等级 INSERT INTO salarygrade VALUES (1,7000,12000), (2,12010,14000), (3,14010,20000), (4,20010,30000), (5,30010,99990) -- 需求: -- 1.查询所有员工信息。查询员工编号，员工姓名，工资，职务名称，职务描述 /* 1.查询两张表 2.条件是emp.job_id = job.id */ SELECT t1.id,-- 员工编号 t1.ename,-- 员工姓名 t1.salary,-- 工资 t2.jname,-- 职务名称 t2.description -- 植物描述 FROM emp t1, job t2 WHERE t1.job_id = t2.id -- 2.查询员工编号，员工姓名，工资，职务名称，职务描述，部门名称，部门位置 /* 1.查询三张表 2.条件是emp.job_id = job.id and emp.dept_id = dept.id */ SELECT t1.id,-- 员工编号 t1.ename,-- 员工姓名 t1.salary,-- 工资 t2.jname,-- 职务名称 t2.description,-- 植物描述 t3.dname,-- 部门名称 t3.loc -- 部门位置 FROM emp t1, job t2, dept t3 WHERE t1.job_id = t2.id AND t1.dept_id = t3.id -- 3.查询员工姓名，工资，工资等级 /* 1.查询两张表emp表和salarygrade 2.条件是emp.salary >= salarygrade.losalary and emp.salary <= salarygrade.hisalary(表之间没有关联不能用等值来进行判断了) 3.简化上一步emp.salary BETWEEN salarygrade.losalary and salarygrade.hisalary */ SELECT t1.ename, t1.salary, t2.grade FROM emp t1, salarygrade t2 WHERE t1.salary BETWEEN t2.losalary AND t2.hisalary -- 4.查询员工姓名，工资，职务名称，职务描述，部门名称，部门位置，工资等级 /* 1.员工名称，工资emp，职务名称，职务描述job,部门名称，部门位置dept，工资等级salarygrade 2.条件emp.job_id = job.id and emp.dept_id = dept.id and emp.salary BETWEEN salarygrade.losalary and salarygrade.hisalary */ SELECT t1.ename, t1.salary, t2.jname, t2.description, t3.dname, t3.loc, t4.grade FROM emp t1, job t2, dept t3, salarygrade t4 WHERE t1.job_id = t2.id AND t1.dept_id = t3.id AND t1.salary BETWEEN t4.losalary AND t4.hisalary -- 5.查询出部门编号、部门名称、部门位置、部门人数 /* 1.部门编号、部门名称、部门位置dept,部门人数 emp表 2.使用分组查询，按照emp.dept_id完成分组，查询count（id） 3.使用子查询将第二部的查询结果和dept表进行关联查询 */ SELECT t1.id, t1.dname, t1.loc, t2.total FROM dept t1, ( SELECT dept_id, COUNT( id ) total FROM emp GROUP BY dept_id ) t2 WHERE t1.id = t2.dept_id -- 6.查询所有员工的姓名及其直接上级的姓名,没有领导的员工也需要查询 /* 1.姓名 emp，直接上级的姓名 emp * emp的id和mgr是自关联的 2.条件 emp.id = emp.mgr 3.查询左表的所有数据，和交集数据 *使用左外连接查询 */ SELECT t1.ename, t1.mgr, t2.id, t2.ename FROM emp t1 LEFT JOIN emp t2 ON t1.mgr = t2.id
