MYSQL的分组查询笔记

CREATE TABLE dept( /*部门表*/
deptno MEDIUMINT   UNSIGNED  NOT NULL  DEFAULT 0, 
dname VARCHAR(20)  NOT NULL  DEFAULT "",
loc VARCHAR(13) NOT NULL DEFAULT ""
);
 
INSERT INTO dept VALUES(10, 'ACCOUNTING', 'NEW YORK'), 
(20, 'RESEARCH', 'DALLAS'), 
(30, 'SALES', 'CHICAGO'), 
(40, 'OPERATIONS', 'BOSTON');
 
SELECT * FROM dept;
 
-- 员工表
 
CREATE TABLE emp
(empno  MEDIUMINT UNSIGNED  NOT NULL  DEFAULT 0, /*编号*/
ename VARCHAR(20) NOT NULL DEFAULT "", /*名字*/
job VARCHAR(9) NOT NULL DEFAULT "",/*工作*/
mgr MEDIUMINT UNSIGNED ,/*上级编号*/
hiredate DATE NOT NULL,/*入职时间*/
sal DECIMAL(7,2)  NOT NULL,/*薪水*/ 	
comm DECIMAL(7,2) ,/*红利 奖金*/
deptno MEDIUMINT UNSIGNED NOT NULL DEFAULT 0 /*部门编号*/
);
 
-- 添加测试数据
 INSERT INTO emp VALUES(7369, 'SMITH', 'CLERK', 7902, '1990-12-17', 800.00,NULL , 20), 
(7499, 'ALLEN', 'SALESMAN', 7698, '1991-2-20', 1600.00, 300.00, 30),  
(7521, 'WARD', 'SALESMAN', 7698, '1991-2-22', 1250.00, 500.00, 30),  
(7566, 'JONES', 'MANAGER', 7839, '1991-4-2', 2975.00,NULL,20),  
(7654, 'MARTIN', 'SALESMAN', 7698, '1991-9-28',1250.00,1400.00,30),  
(7698, 'BLAKE','MANAGER', 7839,'1991-5-1', 2850.00,NULL,30),  
(7782, 'CLARK','MANAGER', 7839, '1991-6-9',2450.00,NULL,10),  
(7788, 'SCOTT','ANALYST',7566, '1997-4-19',3000.00,NULL,20),  
(7839, 'KING','PRESIDENT',NULL,'1991-11-17',5000.00,NULL,10),  
(7844, 'TURNER', 'SALESMAN',7698, '1991-9-8', 1500.00, NULL,30),  
(7900, 'JAMES','CLERK',7698, '1991-12-3',950.00,NULL,30),  
(7902, 'FORD', 'ANALYST',7566,'1991-12-3',3000.00, NULL,20),  
(7934,'MILLER','CLERK',7782,'1992-1-23', 1300.00, NULL,10);
 
SELECT * FROM emp;
 
-- 工资级别
#工资级别表
CREATE TABLE salgrade
(
grade MEDIUMINT UNSIGNED NOT NULL DEFAULT 0, /*工资级别*/ 
losal DECIMAL(17,2)  NOT NULL, /* 该级别的最低工资 */
hisal DECIMAL(17,2)  NOT NULL /* 该级别的最高工资*/
);
 
INSERT INTO salgrade VALUES (1,700,1200);
INSERT INTO salgrade VALUES (2,1201,1400);
INSERT INTO salgrade VALUES (3,1401,2000);
INSERT INTO salgrade VALUES (4,2001,3000);
INSERT INTO salgrade VALUES (5,3001,9999);
 
SELECT * FROM salgrade;
SELECT * FROM dept;
SELECT * FROM emp;
 
--  显示每个部门的平均工资和最低工资
select avg(sal),min(sal),deptno from emp group by deptno;
-- 显示每个部门的每种岗位的平均工资和最低工资
select avg(sal),min(sal),deptno,job from emp group by deptno,job;
select avg(sal),min(sal),deptno,job from emp group by job,deptno;

-- 显示平均工资低于2000的部门号和它的平均工资 //别名
select avg(sal),deptno from emp group by deptno having avg(sal)<2000
select avg(sal) as avg_sal,deptno from emp group by deptno having avg_sal<2000 
-- 显示各个部门的平均工资
select avg(sal),deptno from emp group by deptno;

-- dual 压元表
select INSTR('CHENGSHENGJIE','JIE') from dual;

-- 转大写
select UCASE(ename) from emp;

-- 替换
select ename,REPLACE(job,'MANAGER','经理') from emp;

-- 取指定长度字符
select SUBSTRING(ename,1,2) from emp;

select concat(lcase(substring(ename,1,1)),substring(ename,2)) from emp;

-- 绝对值
select abs(-2) from dual;
-- 十进制转化为二进制
select bin(8) from dual;
-- 向上取整
select ceiling(1.8) from dual;
-- 向下取整
select floor(1.2) from dual;
-- 进制转换,10进制的8转化为2进制
select conv(8,10,2) from dual;
-- 保存小数点后几位
select format(87.569856,3) from dual;
-- 求最小值
select least(0.1,-1,6,89) from dual;

-- 随机数,rand(seed),当不给seed时，每次产生一个随机数，加上一个种子每次产生的随机数是一样的
select rand(2) from dual;