diff --git "a/29 \350\267\257\347\216\262/20231017 \347\252\227\345\217\243\345\207\275\346\225\260\351\207\215\345\201\232.md" "b/29 \350\267\257\347\216\262/20231017 \347\252\227\345\217\243\345\207\275\346\225\260\351\207\215\345\201\232.md" new file mode 100644 index 0000000000000000000000000000000000000000..d38094ec792c461332266ee2353d8e940559186a --- /dev/null +++ "b/29 \350\267\257\347\216\262/20231017 \347\252\227\345\217\243\345\207\275\346\225\260\351\207\215\345\201\232.md" @@ -0,0 +1,475 @@ +# 笔记 + +### 数学函数 + +```sql +-- 绝对值abs() +select abs(-4) -- 4 + +-- 向上取整 ceil(值) +select ceil(1.5) -- 2 + +-- 向下取整 floor(值) +select floor(1.5) -- 1 + +-- 随机数 rand() +select floor(rand()*100) + +-- 四舍五入，截取 round(值，保留点后n位) +select round(1.6666); +select round(1.6666,2); + +-- 截取 truncate(值,保留点后n位) + +``` + + + +### 字符串函数 + +```sql +-- 字符个数 +select char_length('abc') -- 3 +select char_length('软件工程') -- 4 + +-- 拼接字符串 +select concat('你','好','帅哥') +select concat_ws(',','你','好','帅哥') -- 第一个字符为分隔符 + +-- 去空 +select ltrim(' aaa'); +select rtrim('aaa '); +select trim(' aaa ') + +-- 截取 +select substr('hello',2,3); + +-- 获取子串在字符串的位置 +select position('a' in 'abc'); + +-- 替换 +select replace('aaabbbccc','a','1'); + +``` + + + +### 日期函数 + +```sql +-- 获取当前日期 +select curdate(); + +-- 获取当前时间 +select curtime(); + +-- 获取当前日期时间 +select now(); + +-- 从日期字符串获取日期 +select date('2000-02-02'); +select date('2000-02-02 12:12:12'); -- 只获取日期 + +-- 天数差 +select datediff('2001-02-02','2000-02-02'); -- 前减后 + +-- 指定差 +select timestampdiff(day,'2001-02-02','2000-02-02'); -- 后减前 + +-- 日期减法 +select subdate('2001-02-02',interval 2 day); + +-- 日期加法 +select adddate('2001-02-02',interval 2 day); + +-- 获取某日期中的值 +select year('2001-02-02'); +select day('2001-02-02'); +select dayofyear('2001-02-02'); +select dayofweek('2001-02-02'); + +-- 获取该月最后一天 +select last_day('2001-02-02'); + +-- 日期格式 +select date_format('2001-02-02','%Y') + +``` + +http://www.manongjc.com/detail/29-ensoneygersabbx.html + + + +# 控制流函数 + +```sql +-- if(表达式,值1,值2) true返回值1，false返回值2 +select if(1<2,1,2); + +-- ifnull(值1，值2) 如果值1不为null，返回值1，否则返回值2 +select ifnull(null,2); +select ifnull(1,2); + +-- isnull(表达式) 返回1或0 +select isnull(null); +select isnull(''); + +-- nullif(值1，值2) 比较两个值（字符串）,如果当等返回null，否则返回值1 +select nullif(25,25); +``` + +```sql +-- case when +/* +语法1： +case + when 条件表达式1 then 值1 + when 条件表达式2 then 值2 + ... + else 值n +end + +语法2： +case 表达式 + when 条件值1 then 返回值1 + when 条件值2 then 返回值2 + ... + else 返回值n +end + +*/ +``` + + + +# 窗口函数 + +mysql 8.0新增窗口函数（开窗函数）。 + +非聚合窗口函数：是相对于聚合函数来说的，特性为非聚合。一次只处理一行数据。 + +窗口聚合函数：窗口聚合函数在单元行上计算某个字段的结果时，可将窗口范围内的数据输入到聚合函数中，并且不会改变行数。 + + + +### 语法 + +```sql +窗口函数名称(参数) over(partition by ... order by... 窗口大小) +``` + +partition by 分组,等价于group by + +order by 排序 + + + +### 序号函数 + +row_number()、rank()、dense_rank() + + + +### 开窗聚合函数 + +```sql +sum()|avg()|min()|max()|count()| over (partition by ... order by...) +``` + +#### 窗口大小 + +```sql +# 开窗范围 +# 获取各部门薪金总和(范围：初始行至当前行) +select ename,hiredate,deptno,sal, +sum(sal) over(partition by deptno rows between unbounded preceding and current row) 'sum' +from emp; + +-- rows 启用窗口大小 +-- between ... and ... 范围区间 +-- unbounded preceding 起始行 +-- current row 当前行 +``` + +不同案例： + +```sql +# 范围：前3行 + 当前行 +sum(sal) over(partition by deptno rows between 3 preceding and current row) + +# 范围：前3行 + 当前行 + 后1行 +sum(sal) over(partition by deptno rows between 3 preceding and 1 following) +-- following指当前行之后的行 + +# 范围：当前行至最后一行 +sum(sal) over(partition by deptno rows between current row and unbounded following) +-- unbounded following 最终行 +``` + + + +### 分布函数 + +##### cume_dist() + +分组内 <= 或 >= 当前值的行数占比(包含当前值本身) + +```sql +# 查询各部门员工小于等于当前薪资的比例 + +select ename,deptno,sal, +cume_dist() over(partition by deptno order by sal) '占比' +from emp; + +-- order by 控制计算的列 +-- asc 小于等于 +-- desc 大于等于 +``` + + + +### 前后函数 + +返回当前行的前某一行的值，或者后某一行的值 + +lag(列名，前第n行) + +lead(列名，后第n行) + +```sql +select ename,deptno,sal, +lag(sal,1) over(partition by deptno order by sal) '前1', +lag(sal,2) over(partition by deptno order by sal) '前2' +from emp; +``` + + + +### 头尾函数 + +返回第一个或最后一个列的值 + +first_value(列名) + +last_value(列名) + +```sql +-- 查询各个部门中，第一个和最后一个入职的员工姓名 +select ename,deptno,sal,hiredate, +first_value(ename) over(partition by deptno order by hiredate) 'first', +last_value(ename) over(partition by deptno order by hiredate) 'last' +from emp; +``` + + + +### 其他函数 + +nth_value(列名,n) —— 返回截止到当前行，该列的第n个值 + +```sql +-- 查找出各个部门，薪资排名第2的员工姓名 +select ename,deptno,sal, +nth_value(ename) over(partition by deptno order by sal) '第二名' +from emp; + +-- 查询全公司，薪资排名第2的员工姓名 +-- 1 +select ename,deptno,sal, +nth_value(ename,2) over(order by sal) '第二名' +from emp; +-- 2 +select ename,deptno,sal, +nth_value(ename,2) over() '第二名' +from emp order by sal; +``` + +ntile(n) —— 将分区中的有序数据分为n个等级，记录等级数 + + + + + + + +# 作业 + +```mysql +create database work2_21 charset utf8; +use work2_21; +create table if not exists `employee` +( + `eid` int not null auto_increment comment '员工id' primary key, + `ename` varchar(20) not null comment '员工名称', + `dname` varchar(50) not null comment '部门名称', + `hiredate` datetime not null comment '入职日期', + `birth` date not null comment '生日', + `salary` double null comment '基本薪资', + `start_sal` double null comment '入职薪资' +); + +insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('傅嘉熙', '开发部', '2002-08-20 12:00:04','1980-12-10', 9000,6500); +insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('武晟睿', '开发部', '2002-06-12 13:54:12', '1984-2-5',9500,6000); +insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('孙弘文', '开发部', '2003-10-16 08:27:06','1979-8-7', 9400,8000); +insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('潘乐驹', '开发部', '2004-04-22 03:56:11','1980-5-12', 9500,6800); +insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('潘昊焱', '人事部', '2007-02-24 03:40:02','1987-2-12', 5000,4500); +insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('沈涛', '人事部', '2012-12-14 09:16:37','1993-4-30', 6000,5500); +insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('江峻熙', '人事部', '2018-05-12 01:17:48','1990-6-8', 5000,3000); +insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('陆远航', '人事部', '2018-04-14 03:35:57','1989-11-13', 5500,5000); +insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('姜煜祺', '销售部', '2020-03-23 03:21:05','1995-1-1', 6000,5500); +insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('邹明', '销售部', '2015-11-23 23:10:06','1996-2-19', 6800,6000); +insert into `employee` (`ename`, `dname`, `hiredate`, `birth`,`salary`,`start_sal`) values ('董擎苍', '销售部', '2012-02-12 07:54:32','1985-10-7', 6500,4800); +insert into `employee` (`ename`, `dname`, `hiredate`,`birth`, `salary`,`start_sal`) values ('钟俊驰', '销售部', '2010-04-10 12:17:06','1981-3-25', 6000,3500); + + +-- 员工按工龄，每年增加50元薪水。实发薪资 = 基本薪资 + 工龄 * 50 + +### -- 窗口函数 +select * from employee; +#求每个部门的员工总数 +select distinct dname 部门,count(dname) over(partition by dname) 员工总数 from employee; + +#求每个部门的平均工资 +select distinct dname 部门,avg(salary) over(partition by dname) 平均工资 from employee; + +#求每个部门的工资排名（从高到低,相同工资并列，并执行跳过排序） +select dname 部门,rank() over(partition by dname order by salary desc) + 工资排名,salary 工资 from employee; + -- rank():相同工资并列，并执行跳过排序 + -- 高到低 desc + +#求公司所有员工的年龄排序（相同年龄并列，执行跳过排序） +select ename 员工姓名,rank() over(order by birth) ,birth from employee; + +#求每个部门的员工工龄排序（相同年龄并列，执行顺序排序） +select ename 员工姓名,dense_rank() over(partition by dname order by hiredate),hiredate from employee; +-- dense_rank:相同年龄并列，执行顺序排序 + +#计算每个员工的工资与该部门平均工资的差额 +select ename,dname,salary, avg(salary) over(partition by dname) ,(salary-avg(salary) over(partition by dname)) from employee; + +#按员工工资进行排序，比较相邻两个员工的工资，输出比较高的工资------- + + select max(salary) over(partition by salary order by salary rows between unbounded preceding and 1 following ) + from employee ; +-- unbounded preceding 起始行 +-- 1 following 后1行 + +#按员工工资进行排序，查询当前员工与前一位和后一位的工资平均值 + +select * from employee; +select avg(salary) over(partition by ename order by salary rows between 1 preceding and 1 following) +FROM employee ; + + -- 1 preceding 前一行 + +#按员工工资进行排序，查询当前员工至最后一位员工的工资总和 + +select ename,salary,sum(salary) over(partition by salary order by salary rows between current row and unbounded following) from employee ; + +-- current row 当前行 +-- unbounded following 最后一行 + +#计算每个部门内最高薪资与平均薪资的差额 + +select dname,max(salary) over(partition by dname)-avg(salary) over(partition by dname) 差额 from employee; + +#找出各部门年薪第二高的员工 + +select * from employee;-- 开发部有两个人的工资一样 +select dname,nth_value(ename,2) over(partition by dname order by salary) '第二' from employee; + +-- nth_value(列名,n) —— 返回截止到当前行，该列的第n个值 + +#查询各部门中小于等于当前员工实际薪资的比例 + +select ename,dname,salary, cume_dist() over(partition by dname order by start_sal) from employee; + +-- cume_dist()：分组内 <= 或 >= 当前值的行数占比(包含当前值本身) +-- order by 控制计算的列 +-- asc 小于等于 +-- desc 大于等于 + +#查询每个员工工资在全部员工中的排名比例(/等级) + +select ename,salary,ntile(3) over(partition by salary order by salary) '排名比例' from employee; + +-- 按照不同dname字段的值将每个PARTITION分区的数据从小到大分为3个等级 +-- ntile(n) —— 将分区中的有序数据分为n个等级，记录等级数 + +#查询每个部门工资排名在前25%的员工记录数-- + +with a as +(select dname,cume_dist() over(partition by dname order by salary desc) b from employee) +select *,count(b) over(partition by dname) 员工记录数 from a where b=0.25; + +#每个部门按年龄进行排序，求当前员工与前一位员工的年龄差----- +select * from employee; +select sum(year(birth)) over(partition by dname order by year(birth) rows between current row and 1 preceding) from employee ; + +-- current row 当前一行 +-- 1 preceding 前一行 + +#按入职日期进行排序，查询公司每个员工与后面一个员工的入职天数差异------------------- + +select ename, over(order by hiredate rows between current row and 1 following) from employee; + +#将每个部门的员工按工资平均分为2个组，组1为低工资，组2为高工资 + +select ename,salary,num,case when num=1 then '低工资' else '高工资' end '等级' from (select dname,ename,salary,ntile(2) over(order by salary) num from employee) e; +-- 只有case能在select语句中用 +-- end '等级' 可把判断结果单独弄出一列 + +#将所有员工按照工龄分为4个组，并统计每个组的人数 + +select num,count(num) from (select ntile(4) over(order by hiredate) num from employee) e group by num ; + +#将员工按照工资分为3个组，并统计组别，每组平均工资，工资范围（first_value、last_value） + +select num,avg(salary),min(salary),max(salary) from (select salary, ntile(3) over (order by salary) num from employee) b group by num; + +### -- 非窗口函数 + +#按照工龄区分等级，小于5年为新员工,5-15年为老员工,大于15年为骨灰级员工,输出姓名，部门，工龄，级别 + +select ename,dname, +ceil(datediff(now(),hiredate)/365) 工龄, +case when floor(datediff(curdate(),hiredate)/365)<5 then '新员工' when floor(datediff(curdate(),hiredate)/365)>15 then '老员工' else '骨灰级员工' end '等级' +from employee ; + +-- CURDATE() 函数返回当前的日期。 +-- 向上取整 ceil(值) +-- 天数差 +-- select datediff('2001-02-02','2000-02-02'); -- 前减后 + +#返回员工的实际年龄，如果小于当前日期则减1岁 + +select ename,ceil(datediff(now(),birth)/365)-case when datediff(curdate(),365)