2023_10_10_MYSQL_DAY_02_笔记

可用于本人这个头像 · 发表于 2023-10-11 07:09:38

#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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来源:https://www.cnblogs.com/Qinyyds/p/17756058.html
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