2023_10_10_MYSQL_DAY_02_笔记



#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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