2023_10_14_MYSQL_DAY_05_笔记

 https://www.cnblogs.com/tdskee/p/16536166.html
{
   MySQL的优化多种方法（至少15条）
}
 
#查看触发器
show triggers;
#删除触发器
drop trigger 触发器名;
#建立触发器
drop trigger if exists dept_del;
create trigger dept_del after delete on dept for each row
begin
    delete from emp where deptno=old.deptno;
end;
 
#删除外键约束
ALTER TABLE emp DROP FOREIGN KEY  fk_deptno ; 
 
#存储过程调用
CALL `getsalbydeptno`(20,@aaa);
SELECT @aaa;
 
#存储过程创建
DELIMITER $$
USE `sjkxtgl3`$$
DROP PROCEDURE IF EXISTS `getsalbydeptno`$$
CREATE DEFINER=`root`@`localhost` PROCEDURE `getsalbydeptno`(IN dno INT,OUT salsum DECIMAL(7,2))
    BEGIN
       SELECT SUM(sal) INTO salsum FROM emp WHERE deptno=dno;
    END$$
DELIMITER ;
 
 
#建立索引
CREATE INDEX diseasename_index2 ON disease_back2(diseasename);
 
# 88185条疾病名称数据 索引前用时:0.080sec  索引后用时:0.001sec 
SELECT * FROM disease_back2 WHERE diseaseName='轻度酒精中毒' 
 
测试索引
 
CREATE TABLE disease_back AS 
SELECT * FROM disease;
 
CREATE TABLE disease_back2 AS 
SELECT * FROM disease_back;
 
INSERT INTO disease_back 
SELECT * FROM disease_back2
 
INSERT INTO disease_back2 
SELECT * FROM disease_back
 
SELECT * FROM disease WHERE diseaseName='轻度酒精中毒'
 
SELECT * FROM disease_back WHERE diseaseName='轻度酒精中毒'
 
SELECT * FROM disease_back2 WHERE diseaseName='轻度酒精中毒'
 
14章课后作业
 
CREATE TABLE xi( 
    xid  INT PRIMARY KEY AUTO_INCREMENT,
    xname VARCHAR(10) UNIQUE,
    xhead VARCHAR(10) NOT NULL,
    xloc  VARCHAR(30) DEFAULT '浑南区'
);
CREATE TABLE class02( 
    cno  INT PRIMARY KEY AUTO_INCREMENT,
    cname VARCHAR(10) UNIQUE,
    ctype VARCHAR(10) CHECK (ctype IN ('Java班','UI班')),
    xid  INT,
    FOREIGN KEY(xid)  REFERENCES xi(xid) 
);
 
# DEFAULT 使用
CREATE TABLE student9( 
    id  int  PRIMARY KEY,
    sno  int ,
    name varchar(10),
    city varchar(20) DEFAULT '沈阳'
);
INSERT INTO student9(id,sno,name) VALUES(10,20220101,'张三');
 
#检查性约束
CREATE TABLE student8( 
    id  INT PRIMARY KEY ,
    sno  INT ,
    NAME VARCHAR(10),
    gender CHAR(2) CHECK (gender IN ('男','女')),
    age INT CHECK (age >= 15 AND age <=30)
);
 
INSERT INTO student8(id,sno,NAME,gender,age) VALUES(10,20220101,'张三','F',70);
 
#建立表时加入 外键约束
CREATE TABLE student7 ( 
  id INT PRIMARY KEY,
  sno INT,
  sname VARCHAR(10),
  classid INT,
  FOREIGN KEY(classid) REFERENCES class(id)
);
 
#先建立父表
CREATE TABLE class ( 
   id INT PRIMARY KEY,
   cname VARCHAR(20)
);
 
 
#建立表时加入 非空约束
CREATE TABLE student6( 
    id  int PRIMARY KEY ,
    sno  int ,
    sname varchar(10) NOT NULL
);
 
ALTER TABLE student6 MODIFY sno int NOT NULL;
 
#建立表时加入 唯一性约束
CREATE TABLE student4( 
    id  INT PRIMARY KEY AUTO_INCREMENT  ,
    sno  INT ,
    sname VARCHAR(10),
    idCard CHAR(18) UNIQUE
);
# 唯一性约束 可以为空
INSERT INTO student4(id,sno,sname,idcard) VALUES(3,20220103,'王五',NULL);
INSERT INTO student4(id,sno,sname,idcard) VALUES(4,20220104,'赵六',NULL);
 
# 自增长类型 默认从1开始 每次+1
AUTO_INCREMENT
 
#删除主键约束
ALTER TABLE student2 DROP PRIMARY KEY;
 
#建立表时无主键约束 追加主键约束
CREATE TABLE student2 ( 
   id INT,
   sno INT,
   sname VARCHAR(10)
);
#追加主键
ALTER TABLE student2 ADD PRIMARY KEY(id);
 
#建立表时加入 主键约束
CREATE TABLE student1 ( 
   id INT PRIMARY KEY,
   sno INT,
   sname VARCHAR(10)
);
 
 
#截断表
TRUNCATE TABLE dept_copy202;
 
#修改表名
RENAME TABLE dept_copy2 TO dept_copy202;
 
#删除列
ALTER TABLE dept_copy2 DROP interest;
 
#修改列名
ALTER TABLE dept_copy2 CHANGE hobby interest VARCHAR(100);
 
#改变表 修改一个字段
ALTER TABLE dept_copy2 MODIFY hobby VARCHAR(200);
 
#改变表 加一个字段
ALTER TABLE dept_copy2 ADD hobby VARCHAR(100);
 
#删除表
DROP TABLE dept_copy;
DROP TABLE IF EXISTS dept_copy;
 
#复制表结构和数据
CREATE TABLE dept_copy2 SELECT * FROM dept;
 
#复制表结构
CREATE TABLE dept_copy LIKE dept;
 
#查看表结构
DESC emp;
 
#建表语句
CREATE TABLE student( 
  sno int,
  sname varchar(10),
  gender char(1),
  birthday date
)
 
#查看当前数据库中的表
SHOW TABLES;
 
#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;
 
#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;
 
#建立数据库命令
CREATE DATABASE db1;
CREATE DATABASE  IF  NOT  EXISTS  db1;
 
 
 
11章 作业题01答案
SET autocommit=0;
SHOW VARIABLES LIKE 'autocommit';
 
INSERT INTO copy_emp VALUES(6789,'WANGWU','2000-1-1',50,NULL);
COMMIT;
 
INSERT INTO copy_emp 
SELECT empno,ename,hiredate,deptno,sal FROM emp WHERE deptno=10;
 
UPDATE copy_emp SET sal=sal*1.2 WHERE deptno=10;
ROLLBACK;
 
UPDATE copy_emp SET sal=sal*1.2 WHERE deptno=10;
 
 
#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;
 
#事务操作
START TRANSACTION;
INSERT INTO dept(deptno,dname,loc) VALUES(18,'dept1','loc1');
SELECT * FROM dept;
ROLLBACK;
SELECT * FROM dept;
 
#查看事务提交状态
SHOW VARIABLES LIKE 'autocommit';
#关闭事务的自动提交
SET autocommit=0;
 
事务：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  ***????  mysql不支持 需要建立临时表
 
DELETE FROM emp_back
WHERE empno IN (SELECT empno 
FROM emp a ,(SELECT deptno,AVG(sal) Sa FROM emp GROUP BY deptno) b
WHERE a.`deptno`= b.deptno AND a.`sal` > b.Sa);
 
DELETE FROM emp z WHERE sal>(SELECT AVG(sal) FROM emp WHERE deptno=z.deptno);
 
SELECT empno FROM emp z WHERE sal>(SELECT AVG(sal) FROM emp WHERE deptno=z.deptno);
 
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