2023_10_11_MYSQL_DAY_03_笔记_下

#截断表的作用是把原来的表摧毁，重新创建一个结构和原来一模一样的新表，语法如下：
TRUNCATE TABLE table;
#TRUNCATE和DELETE区别
#1、TRUNCATE是DDL命令，使用ROLLBACK不可以回滚。而DELETE是DML命令，使用ROLLBACK可以回滚。
#2、DELETE可以通过指定删除条件实现部分删除，TRUNCATE不能指定条件。




#修改字符集
ALTER TABLE 表名 character set 字符集;

#修改表名
RENAME TABLE 表名 TO 新表名;

RENAME TABLE dept_copy2 TO dept_copy1;



#删除列
ALTER TABLE 表名 DROP 列名;
ALTER TABLE dept_copy2 DROP interest;


#修改列名
ALTER TABLE 表名 CHANGE 旧列名 新列名 类型;
ALTER TABLE dept_copy2 CHANGE hobby interest VARCHAR(100);


#改变表 修改一个字段
ALTER  TABLE  表名  MODIFY  列名 新的类型;
ALTER TABLE dept_copy2 MODIFY hobby VARCHAR(200);


#改变表 加一个字段
ALTER TABLE 表名 ADD 列名 类型;
ALTER TABLE dept_copy2 ADD hobby VARCHAR(100);




#直接删除表，语法如下：
DROP TABLE 表名;
DROP TABLE dept_copy;

DROP TABLE  IF  EXISTS dept_copy;



#同时复制表结构和数据，语法如下：
CREATE TABLE 新表名 查询语句;
CREATE TABLE dept_copy2 SELECT * FROM dept ;



#仅复制表结构，语法如下：
CREATE TABLE 新表名 LIKE 旧表名;
CREATE TABLE dept_copy LIKE dept;




#查看创建表的SQL语句
SHOW CREATE TABLE 表名;


#查看表结构
DESC 表名;



#查看某个数据库中的所有表
SHOW TABLES;



#MySQL8.0版本开始，数据库默认的字符集是utf8mb4

#使用/切换数据库
USE db1;


#查看正在使用的数据库
SELECT DATABASE();

#删除数据库

DROP  DATABASE  db2;

#注意：数据库删除后，将无法恢复，因此要谨慎操作。

#修改数据库字符集

ALTER  DATABASE  DB1  DEFAULT  CHARACTER  SET  utf8mb4;



#查看某个数据库的定义信息

SHOW  CREATE  DATABASE  DB1;



#显示存在的数据库
SHOW  DATABASES;





#创建数据库命令
CREATE DATABASE DB1;

CREATE DATABASE IF NOT EXISTS DB1 ;



11章 作业题01答案
 
CREATE TABLE copy_emp   (
		empno INT(4),
		ename VARCHAR(20),
		hiredate DATE,
		deptno INT(2),
		sal DOUBLE(8,2)
)


#依次写出下列SQL语句:
#1) 开启一个查询窗口1，设置事务手动提交
SET autocommit = 0 ;
SHOW VARIABLES LIKE  'autocommit';
#2) 在表copy_emp中插入数据，员工编号6789 ，员工姓名WANGWU，sal字段插入空值，部门号50，入职时间为2000年1月1日，并提交事务
INSERT INTO copy_emp VALUES(6789,'WANGWU','2000-1-1',50,NULL);
COMMIT;
#3) 把emp表中部门号为10号部门的员工信息插入到copy_emp表，不做结束事务的操作。
INSERT INTO copy_emp AS SELECT empno ,ename, hiredate ,deptno,sal FROM emp WHERE deptno = 10;

#4) 修改copy_emp表中数据，要求10号部门所有员工涨20%的工资，将题3和题4的SQL语句回滚并查看数据结果
UPDATE copy_emp SET sal=sal*1.2 WHERE deptno = 10 ;
ROLLBACK;
#5) 修改copy_emp表中6789员工的工资更新为3500，不做结束事务的操作。
UPDATE copy_emp SET sal = 3500 WHERE empno = 6789;
#6) 开启一个查询窗口2，设置事务手动提交。
SET autocommit = 0 ;
SHOW VARIABLES LIKE  'autocommit';
SELECT * FROM copy_emp ;
#7) 在查询窗口2中，查看copy_emp表中6789员工工资。
SELECT sal FROM copy_emp WHERE empno = 6789;
#8) 在查询窗口2中，修改copy_emp表中6789员工的工资更新为1500，不做结束事务的操作。
UPDATE copy_emp SET sal = 1500 WHERE empno = 6789;
#10)  在查询窗口1中，commit提交事务，回到查询窗口2中查看结果
COMMIT;





#课堂练习51
START TRANSACTION ;		
UPDATE emp
SET sal = sal-500
WHERE ename="SCOTT";
UPDATE emp
SET sal = sal+200
WHERE ename="SMITH";
UPDATE emp
SET sal = sal+300a
WHERE ename="ALLEN";
ROLLBACK;
#COMMIT;


START TRANSACTION ;		
INSERT INTO dept(deptno,dname,loc) 
VALUES(18, 'dept1','loc1');
SELECT * 
FROM dept;

ROLLBACK;
SELECT * 
FROM dept;
ROLLBACK;


#查看事务的提交状态
SHOW VARIABLES LIKE  'autocommit';

#关闭事务的自动提交
SET autocommit = 0 ;
#打开事务的自动提交
SET autocommit = 1 ;

事务：英文单词Transaction，是由一个或多个SQL语句所组成的操作集合，这些SQL语句作为一个完整的工作单元，要么全部执行成功，要么全部执行失败。




10章 作业题01答案
INSERT INTO class(classid,cname) VALUES(1,'Java1班');
INSERT INTO class(cname,classid) VALUES('Java2班',2);
INSERT INTO class VALUES(3,'Java3班',NULL);

10章 作业题02 03 04答案
INSERT INTO student VALUES('A001','张三','男','2005-5-1',100,1);
INSERT INTO student VALUES('A002','MIKE','男','1905-05-06',10,NULL);
INSERT INTO student(xh,xm,sex)  VALUES('A003','JOHN','女' );

10章 作业题05答案
UPDATE student
SET sex='女'
WHERE xh='A002';

10章 作业题06答案
UPDATE student
SET sex='男',birthday='1980-04-01'
WHERE xh='A003';

10章 作业题07答案
做法1
UPDATE student
SET studentcid=3
WHERE studentcid IS NULL;

做法2
UPDATE student
SET studentcid=(SELECT classid FROM class WHERE cname='Java3班')
WHERE studentcid IS NULL;






#课堂练习50
#删除语句 多列子查询  ***
DELETE FROM emp_back
WHERE (deptno,sal) IN  (SELECT deptno,AVG(sal) FROM emp GROUP BY deptno);

#课堂练习49
#删除语句 使用了子查询
DELETE FROM emp_back
WHERE deptno = (SELECT deptno FROM dept WHERE loc='NEW YORK');

#课堂练习48
DELETE FROM emp_back
WHERE mgr=7566;

#删除语句 
DELETE FROM emp_back
WHERE job='CLERK';

#课堂练习48
#更新语句 使用了子查询
UPDATE manager
SET sal=sal+500
WHERE deptno IN (SELECT deptno FROM dept WHERE loc='NEW YORK' OR loc='CHICAGO');

#课堂练习47
UPDATE manager
SET comm=0.0
WHERE comm IS NULL;

#课堂练习46
UPDATE manager
SET job='CLERK'
WHERE deptno=20;


#更新语句
UPDATE emp
SET deptno=20,comm=1200
WHERE empno=8888;

#课堂练习45
CREATE TABLE emp_back AS 
SELECT * FROM emp WHERE 1=0;

INSERT INTO emp_back 
SELECT * FROM emp WHERE hiredate > '1982-1-1'

#通过子查询插入多行数据
INSERT INTO manager
SELECT * FROM emp WHERE job='MANAGER';

#利用查询语句建立表
CREATE TABLE manager
SELECT * FROM emp WHERE 1=0;

#课堂练习44
INSERT INTO emp(empno,ename,job,mgr,hiredate,sal,comm,deptno)
VALUES (8888,'BOB','CLEAK',7788,SYSDATE(),3000,NULL,NULL);

#使用日期函数插入数据
INSERT INTO emp(empno,ename,job,mgr,hiredate,sal,comm,deptno)
VALUES (7196,'GREEN','SALESMAN',7782,SYSDATE(),2000,NULL,10);

INSERT INTO emp(empno,ename,job,mgr,hiredate,sal,comm,deptno)
VALUES (7197,'GREEN2','SALESMAN',7782,'2023-9-1',2000,NULL,10);

#获取当前时间的系统函数
SELECT SYSDATE();

#课堂练习43
INSERT INTO dept(deptno,dname) VALUES(90,'MARKET');
#课堂练习42
INSERT INTO dept(loc,deptno,dname) VALUES('SY',80,'HR');

#插入语句 方式2
INSERT INTO dept VALUES(201,'宣传部','上海');
#空值的插入
INSERT INTO dept VALUES(203,'后勤部',NULL);


#插入语句 方式1
INSERT INTO dept(loc,deptno,dname) VALUES('河南新乡',200,'研发部');
#空值的插入
INSERT INTO dept(loc,deptno,dname) VALUES(NULL,202,'服务部');
INSERT INTO dept(deptno,dname) VALUES(205,'小麦部');

06章04题作业答案
SELECT e.`ename` ,d.`dname`,e.`sal`,s.`grade`
FROM emp e LEFT OUTER JOIN dept d ON(e.`deptno`=d.`deptno`), salgrade s
WHERE e.`sal` BETWEEN s.`losal` AND s.`hisal` AND s.`grade` > 4


#在 FROM 子句中使用子查询
SELECT  a.ename, a.sal, a.deptno, b.salavg
FROM    emp a, (SELECT   deptno, AVG(sal) salavg
                FROM     emp
                GROUP BY deptno) b
WHERE   a.deptno = b.deptno  AND    a.sal > b.salavg;


#子查询里的空值处理
SELECT    ename
FROM     emp
WHERE  empno NOT IN (SELECT IFNULL (mgr,0) FROM   emp);

#多列子查询
SELECT deptno,ename,hiredate 
FROM emp 
WHERE (deptno,hiredate) IN (SELECT deptno ,MIN(hiredate) 
                            FROM emp 
                            GROUP BY deptno);


#课堂练习41
SELECT ename,job
FROM emp
WHERE job = ANY (SELECT job FROM emp WHERE deptno=10) 
      AND deptno <> 10;
	  
	  

#课堂练习40
SELECT ename,hiredate
FROM emp
WHERE hiredate > ALL (SELECT hiredate FROM emp WHERE deptno=10) 
      AND deptno <> 10;

#课堂练习39
SELECT ename,hiredate
FROM emp
WHERE hiredate > ANY (SELECT hiredate FROM emp WHERE deptno=10) 
      AND deptno <> 10;

#多行子查询 all操作符
SELECT empno, ename, job, sal
FROM     emp
WHERE     sal > ALL (SELECT sal FROM emp WHERE  deptno= 20)
AND    deptno <> 20;

SELECT empno, ename, job, sal
FROM     emp
WHERE     sal < ALL (SELECT sal FROM emp WHERE  deptno= 20)
AND    deptno <> 20;

#多行子查询 any操作符
SELECT ename,sal,empno
FROM emp
WHERE empno < ANY (SELECT mgr FROM emp ORDER BY mgr DESC);

SELECT ename,sal,empno
FROM emp
WHERE empno > ANY (SELECT mgr FROM emp ORDER BY mgr DESC);

SELECT ename,sal,empno
FROM emp
WHERE empno = ANY (SELECT mgr FROM emp ORDER BY mgr DESC);


#多行子查询 in操作符
SELECT ename,sal
FROM emp
WHERE empno IN (SELECT mgr FROM emp);

#课堂练习38
SELECT deptno,AVG(sal)
FROM emp
GROUP BY deptno
HAVING AVG(sal) > (SELECT AVG(sal) FROM emp WHERE deptno=10);

#课堂练习37
SELECT ename,sal,dname
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`
      AND sal > (SELECT sal FROM emp WHERE ename='SMITH')
      AND d.`loc`='CHICAGO';

#课堂练习36
SELECT ename,hiredate
FROM emp
WHERE hiredate = (SELECT MIN(hiredate) FROM emp);


# HAVING子句中使用子查询
SELECT  deptno, MIN(sal)
FROM    emp
GROUP BY  deptno
HAVING    MIN(sal) > (SELECT MIN(sal) FROM  emp WHERE deptno = 20);


#子查询中使用组函数
SELECT ename,job,sal
FROM emp
WHERE sal = (SELECT MIN(sal) FROM emp);

#单行子查询语句
SELECT ename,job
FROM emp
WHERE job = (SELECT job FROM emp WHERE empno=7369)
     AND sal > (SELECT sal FROM emp WHERE empno=7876);

#子查询 单行子查询
SELECT ename
FROM emp
WHERE sal > (SELECT sal FROM emp WHERE ename='JONES');


#课堂练习35
SELECT ename,hiredate,deptno
FROM emp
LIMIT 0,5; #第1页

SELECT ename,hiredate,deptno
FROM emp
LIMIT 5,5; #第2页

SELECT ename,hiredate,deptno
FROM emp
LIMIT 10,5; #第3页


#课堂练习34
SELECT e.deptno,dname,COUNT(*),AVG(sal)
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`
GROUP BY e.deptno,dname
HAVING COUNT(*) > 2 AND AVG(sal) > 2000
ORDER BY COUNT(*);

#七个子句的查询
SELECT job,SUM(sal)
FROM emp
WHERE job NOT LIKE 'SALES%'
GROUP BY job
HAVING SUM(sal) > 5000
ORDER BY SUM(sal)
LIMIT 0,2;

#分页查询
SELECT empno,ename,deptno,sal
FROM emp
ORDER BY empno
LIMIT 5,5; #第2页

SELECT empno,ename,deptno,sal
FROM emp
ORDER BY empno
LIMIT 0,5; #第1页

#课堂练习33
SELECT e.deptno,dname,COUNT(*)
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`
GROUP BY e.deptno,dname
HAVING COUNT(*) > 2;

总结:
1、WHERE子句用来过滤分组之前的记录，不能使用组函数
2、HAVING子句用来过滤分组之后的记录，可以使用组函数

#6个子句的查询
SELECT job,SUM(sal)
FROM emp
WHERE job NOT LIKE 'SALES%'
GROUP BY job
HAVING SUM(sal) > 5000
ORDER BY SUM(sal);

查询语句执行过程：
1、通过FROM子句中找到需要查询的表；
2、通过WHERE子句进行非分组函数筛选判断；
3、通过GROUP BY子句完成分组操作；
4、通过HAVING子句完成组函数筛选判断；
5、通过SELECT子句选择显示的列或表达式及组函数；
6、通过ORDER BY子句进行排序操作。

#HAVING 子句
SELECT deptno,COUNT(empno) 
FROM emp 
GROUP BY deptno
HAVING COUNT(empno) > 3; 

SELECT deptno,MAX(sal)
FROM emp
GROUP BY deptno
HAVING MAX(sal) > 2900;


#课堂练习32
SELECT COUNT(*),MAX(sal),MIN(sal),d.`loc`
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno` AND d.`loc`='CHICAGO'
GROUP BY d.`loc`;




#课堂练习31 自连接
SELECT e2.`empno` 经理编号,e2.`ename` 经理姓名,COUNT(*)
FROM emp e,emp e2
WHERE e.`mgr`=e2.`empno`
GROUP BY e2.`empno`,e2.`ename`;

#课堂练习30
SELECT d.`deptno`,d.`dname`,e.`job`,COUNT(empno),MAX(sal),MIN(sal)
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`
GROUP BY d.`deptno`,d.`dname`,e.`job`;

#多表查询分组查询
SELECT d.`deptno`,d.`dname`,COUNT(empno),MAX(sal)
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`
GROUP BY d.`deptno`,d.`dname`;


#按多列分组查询
SELECT deptno,job,SUM(sal)
FROM emp
GROUP BY deptno,job;

#分组子句 
SELECT job,COUNT(empno)
FROM emp
GROUP BY job;

SELECT deptno,AVG(sal)
FROM emp
GROUP BY deptno;

#课堂练习29
SELECT COUNT(*),MAX(sal),MIN(sal)
FROM emp 
WHERE deptno=30;

#课堂练习28
SELECT (sal+IFNULL(comm,0))*12 年收入
FROM emp 

#课堂练习27
SELECT COUNT(job), COUNT(DISTINCT job)
FROM emp 


#课堂练习26
SELECT SUM(sal),AVG(sal)
FROM emp
WHERE deptno=20;

#除COUNT(*)之外，其它所有分组函数都会忽略列中的空值，然后再进行运算; IFNULL==空值处理函数
SELECT AVG(comm),AVG(IFNULL(comm,0))
FROM emp;

#空值处理函数 IFNULL(comm,0)
SELECT ename 员工姓名,sal 工资收入,comm 奖金收入,sal+IFNULL(comm,0) 总收入 
FROM emp;

SELECT COUNT(deptno),COUNT(DISTINCT deptno)
FROM emp

#五个组函数--聚合函数
SELECT MIN(hiredate),MAX(hiredate),MIN(sal),MAX(sal),AVG(sal),SUM(sal),COUNT(*)
FROM emp;

#课堂练习25
SELECT e.empno,e.ename,e.`job`,d.deptno,d.`loc`
FROM emp e,dept d 
WHERE e.deptno = d.deptno AND (d.`loc`='CHICAGO' OR job='MANAGER');


#联合查询 UNION 去除重复数据
SELECT e.empno,e.ename,d.deptno,d.dname 
FROM emp e LEFT OUTER JOIN dept d ON(e.deptno = d.deptno)
UNION 
SELECT e.empno,e.ename,d.deptno,d.dname 
FROM emp e RIGHT OUTER JOIN dept d ON(e.deptno = d.deptno);

#联合查询  UNION ALL 保留重复数据
SELECT e.empno,e.ename,d.deptno,d.dname 
FROM emp e LEFT OUTER JOIN dept d ON(e.deptno = d.deptno)
UNION ALL
SELECT e.empno,e.ename,d.deptno,d.dname 
FROM emp e RIGHT OUTER JOIN dept d ON(e.deptno = d.deptno);


#课堂练习24 右外连接  题目?   没有下属的也要查出来
SELECT e.`ename` ,e2.`ename`
FROM emp e RIGHT OUTER JOIN emp e2 ON(e.`mgr`=e2.`empno`);


#课堂练习23 左外连接  没有领导的也要查出来
SELECT e.`ename` ,e2.`ename`
FROM emp e LEFT OUTER JOIN emp e2 ON(e.`mgr`=e2.`empno`);


#课堂练习22
SELECT ename,dname,hiredate
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno` AND e.`hiredate` > '1980-5-1'

#课堂练习21 笛卡尔积数据
SELECT ename,dname
FROM emp,dept


#右外连接
SELECT e.`ename` ,e.`deptno`,d.`loc`
FROM emp e RIGHT OUTER JOIN dept d ON(e.`deptno`=d.`deptno`);


#左外连接
SELECT e.`ename` ,e.`deptno`,d.`loc`
FROM emp e LEFT OUTER JOIN dept d ON(e.`deptno`=d.`deptno`);

#等值连接 自然连接
SELECT e.`ename` ,e.`deptno`,d.`loc`
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`


#课堂练习20 自连接
SELECT e.`ename` 员工姓名,e.`empno` 员工编号,e2.`ename` 经理姓名,e2.`empno` 经理编号
FROM emp e,emp e2,dept d
WHERE e.`mgr`=e2.`empno` AND e.`deptno`=d.`deptno` AND (d.`loc`='NEW YORK' OR  d.`loc`='CHICAGO');

#自连接
SELECT e.`ename` 员工姓名,e2.`ename` 上级姓名
FROM emp e,emp e2
WHERE e.`mgr`=e2.`empno`

#课堂练习19
SELECT e.`empno`,e.`ename`,e.`sal`,s.`grade`,d.`loc`
FROM emp e,dept d,salgrade s
WHERE e.`deptno`=d.`deptno` AND e.`sal` BETWEEN s.`losal` AND s.`hisal`
ORDER BY s.`grade` DESC;

#多于两个表的连接
SELECT e.`ename`,e.`sal`,d.`dname`,s.`grade`
FROM emp e,dept d,salgrade s
WHERE e.`deptno`=d.`deptno` AND e.`sal` BETWEEN s.`losal` AND s.`hisal`; 

#非等值连接
SELECT ename,sal,grade
FROM emp e,salgrade s
WHERE e.`sal` BETWEEN s.`losal` AND s.`hisal`;

#综合练习4
SELECT ename,e.deptno,dname,sal
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno` AND dname = 'RESEARCH' AND sal < 1500;

#综合练习3
SELECT ename,loc
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno` AND ename LIKE '%A%';

#综合练习2
SELECT ename,comm,loc
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno` AND loc='CHICAGO' AND comm IS NOT NULL;

#综合练习1
SELECT ename,e.deptno,dname
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`


#多表等值连接查询
SELECT empno,ename,dept.deptno,dname
FROM emp,dept
WHERE emp.`deptno`=dept.`deptno`
#使用表的别名
SELECT empno,ename,d.deptno,dname
FROM emp e,dept d
WHERE e.`deptno`=d.`deptno`

#课堂练习18
SELECT ename,hiredate,job
FROM emp
WHERE hiredate BETWEEN '1982-1-1' AND '1983-12-31' AND (job LIKE 'SALES%' OR job LIKE 'MAN%')
ORDER BY hiredate DESC

#课堂练习17
SELECT ename,deptno,sal
FROM emp
WHERE deptno NOT IN (10) AND sal BETWEEN 2000 AND 3000
ORDER BY deptno ASC,sal DESC


#课堂练习16
SELECT ename,deptno,sal
FROM emp
WHERE deptno IN (20,30)
ORDER BY sal

SELECT ename,deptno
FROM emp
WHERE deptno IN (20,30)
ORDER BY sal



#同时按多列排序
SELECT ename,deptno,sal
FROM emp
ORDER BY deptno ASC,sal DESC;

#DESC 降序  从大到小  == 空值小
SELECT ename,job,deptno,hiredate
FROM emp
ORDER BY hiredate DESC

#按三种方式排序
SELECT ename,job,deptno,hiredate
FROM emp
ORDER BY hiredate

SELECT ename,job,deptno,hiredate 入职日期
FROM emp
ORDER BY 入职日期

SELECT ename,job,deptno,hiredate 入职日期
FROM emp
ORDER BY 4


可以按照3种方式进行排序：分别是按列名排序、按列别名排序、按列序号排序。
ASC表示按升序排序(默认值), DESC表示按降序排序。
可以同时按照多个列名进行排序
空值在升序排列中排在最前面，在降序排列中排在最后 == 空值小


4种特殊比较运算符	BETWEEN..AND.. ,  IN,  LIKE,  IS NULL

#课堂练习15
SELECT ename,job,deptno
FROM emp
WHERE job IN ('SALESMAN','MANAGER') AND deptno IN (10,20) AND ename LIKE '%A%';

SELECT ename,job,deptno
FROM emp
WHERE (job ='SALESMAN' OR job='MANAGER') AND (deptno=10 OR deptno=20) AND ename LIKE '%A%';


#课堂练习14
SELECT ename,hiredate,job
FROM emp
WHERE hiredate BETWEEN '1981-1-1' AND '1981-12-31' AND job NOT LIKE 'SALES%';

SELECT ename,hiredate,job
FROM emp
WHERE hiredate >= '1981-1-1' AND hiredate <='1981-12-31' AND job NOT LIKE 'SALES%';

#课堂练习13 写法1 使用特殊比较运算符
SELECT ename,deptno,sal
FROM emp
WHERE deptno IN (10,20) AND sal BETWEEN 3000 AND 5000;
#写法2 使用逻辑运算符
SELECT ename,deptno,sal
FROM emp
WHERE (deptno = 10 OR deptno=20) AND (sal >= 3000 AND sal <= 5000);


#课堂练习12
SELECT ename,job,sal
FROM emp
WHERE sal > 2000 AND (job='MANAGER' OR job='SALESMAN');

#运算符的优先级
SELECT ename, job, sal 
FROM   emp 
WHERE ( job='SALESMAN'  
OR  job='PRESIDENT') 
AND  sal>1500;

SELECT ename, job, sal 
FROM   emp 
WHERE  job='SALESMAN'  
OR  job='PRESIDENT'
AND  sal>1500;


SELECT ename,comm
FROM emp
WHERE comm IS NOT NULL;

SELECT ename,sal
FROM emp
WHERE sal NOT BETWEEN 3000 AND 5000;

NOT BETWEEN .. AND .. :不在某个区间
NOT IN (集合）：不在某个集合内
NOT LIKE    ：不像.....
IS NOT NULL:  不是空


#课堂练习11
SELECT ename,comm
FROM emp
WHERE comm IS NULL;

#课堂练习10
SELECT *
FROM emp
WHERE ename LIKE '%T_';

#课堂练习9
SELECT *
FROM emp
WHERE ename LIKE 'W%';

# IS NULL
SELECT ename,mgr
FROM emp
WHERE mgr IS NULL;


SELECT ename,comm
FROM emp
WHERE comm IS NULL;

#Like运算符
SELECT ename
FROM emp
WHERE ename LIKE 'S%';

SELECT ename
FROM emp
WHERE ename LIKE 'S_';

SELECT ename
FROM emp
WHERE ename LIKE '%A%';

SELECT ename
FROM emp
WHERE ename LIKE '__A%';

#课堂练习8
SELECT ename,sal
FROM emp
WHERE sal BETWEEN 3000 AND 5000;

#课堂练习7
SELECT ename,hiredate
FROM emp
WHERE hiredate BETWEEN '1982-1-1' AND '1985-12-31';

#IN运算符
select empno,ename,deptno
from emp
where deptno in (10,20);

#使用BETWEEN .. AND.. 可以查询出某列的值在某个范围内(包括边界值)的数据行
SELECT empno,ename,sal
FROM emp
WHERE sal BETWEEN 1250 AND 1600;

#课堂练习6
SELECT empno,ename,deptno
FROM emp
WHERE deptno <> 10;

SELECT empno,ename,deptno
FROM emp
WHERE deptno != 10;

#课堂练习5
SELECT empno,ename,hiredate
FROM emp
WHERE hiredate < '1985-12-31';

#课堂练习4
SELECT empno,ename,job
FROM emp
WHERE job='SALESMAN';

#带条件查询2 非等值情况
SELECT empno,ename,hiredate
FROM emp
WHERE hiredate > '1985-01-01';


#带条件查询2
SELECT empno,ename,job
FROM emp
WHERE job='CLERK';

SELECT empno,ename,job
FROM emp
WHERE job="CLERK";

#带条件查询1
SELECT empno,ename,deptno
FROM emp
WHERE deptno=20;

#课堂练习3
SELECT DISTINCT job FROM emp

#排除重复数据的查询
SELECT DISTINCT deptno FROM emp

#课堂练习2  ==?
SELECT ename 员工姓名,sal 工资收入,comm 奖金收入,sal+comm 总收入 FROM emp;

#课堂练习1
SELECT ename,sal 涨薪前,sal*1.2 涨薪后 FROM emp;

#空值参与算术运算，运算后的结果仍为NULL ==待解决?
SELECT ename,sal,comm,sal+comm 月总收入 FROM emp

#数值类型的字段可以做数学运算
SELECT empno,ename,sal,sal*12 年薪 FROM emp

#按字段别名查询  单双引号的使用
SELECT empno 编号,ename "姓 名",sal '工 资',comm "奖,金" FROM emp

#按字段别名查询
SELECT empno 编号,ename 姓名,sal 工资,comm 奖金 FROM emp

#查询指定字段
SELECT empno,ename,sal,comm FROM emp

#查询所有字段
SELECT * FROM emp 

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