多表查询

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左外连接&右外连接

-- 查询emp表所有数据和对应的部门信息
select * from emp left join dept on emp.dep_id = dept.did;-- 右外连接
-- 查询 dept 表所有数据和对应的员工信息select * from emp right join dept on emp.dep_id = dept.did;

内连接

select * from emp where salary > (select salary from emp where name = '猪八戒')-- 多行单列子查询
-- 查询 '财务部' 和 '市场部' 所有员工的信息
select * from emp where dep_id in (select did from dept where dname = '财务部' or dname = '市场部');-- 查询入职日期是 '2011-11-11' 之后的员工信息和部门信息
select * from (select * from emp where join_date > '2011-11-11') t1, dept where t1.dep_id = dept.did;

查询练习

DROP TABLE
IFEXISTS emp;
DROP TABLE
IFEXISTS dept;
DROP TABLE
IFEXISTS job;
DROP TABLE
IFEXISTS salarygrade;-- 部门表
CREATE TABLE dept ( id INT PRIMARY KEY, -- 部门iddname VARCHAR ( 50 ), -- 部门名称loc VARCHAR ( 50 ) -- 部门所在地
) -- 职位表, 职务名称, 职务描述
CREATE TABLE job ( id INT PRIMARY KEY, jname VARCHAR ( 20 ), description VARCHAR ( 50 ) );-- 员工表
CREATE TABLE emp (id INT PRIMARY KEY,-- 员工 idename VARCHAR ( 50 ),-- 员工姓名job_id INT,-- 职务 idmgr 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 ) 
);-- 工资等级表
CREATE TABLE salarygrade ( grade INT PRIMARY KEY, -- 级别losalary INT, -- 最低工资hisalary INT -- 最高工资
);-- 添加4个部门
INSERT INTO dept ( id, dname, loc )
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' );-- 添加4个职务
INSERT INTO job ( id, jname, description )
VALUES( 1, '董事长', '管理整个公司，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', '使用办公软件' );-- 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', '8000.0', NULL, 20 ),( 1002, '卢俊义', 3, 1006, '2001-02-20', '16000.00', '3000.00', 30 ),( 1003, '林冲', 3, 1006, '2001-02-22', '12500.00', '5000.00', 30 ),( 1004, '唐僧', 2, 1009, '2001-04-02', '29750.00', '5000.00', 30 ),( 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 );-- 添加5个工资等级
INSERT INTO salarygrade ( grade, losalary, hisalary )
VALUES( 1, 7000, 12000 ),( 2, 12010, 14000 ),( 3, 14010, 20000 ),( 4, 20010, 30000 ),( 5, 30010, 99990 );-- 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
SELECTemp.id,emp.ename,emp.salary,job.jname,job.description
FROMemp,job 
WHEREemp.job_id = job.id
ORDER BY(emp.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
SELECTemp.id,emp.ename,emp.salary,job.jname,job.description,dept.dname,dept.loc
FROM emp,job,dept
WHERE (emp.job_id = job.id AND emp.dept_id = dept.id)
ORDER BY (emp.id);-- 3、查询员工姓名,工资,工资等级
SELECT emp.ename,emp.salary,t2.grade
FROMemp, salarygrade t2
WHERE emp.salary >= t2.losalary AND emp.salary <= 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
SELECT emp.ename,emp.salary,job.jname,job.description,dept.dname,dept.loc,t3.grade
FROMemp
INNER JOIN job ON emp.job_id = job.id
INNER JOIN dept ON emp.dept_id = dept.id
INNER JOIN salarygrade t3 ON emp.salary BETWEEN t3.losalary AND t3.hisalary;-- 5、查询出部门编号、部门名称、部门位置、部门人数
SELECTdept.id,dept.dname,dept.loc,count(*) count
FROM emp
INNER JOIN dept ON emp.dept_id = dept.id
GROUP BY(dept_id);