标签：运算符 描述 单表 mes char rom 方式 员工 with
目录
#准备表和记录
company.employee #设计表结构
员工id id int
姓名 emp_name varchar
性别 sex enum
年龄 age int
入职日期 hire_date date
岗位 post varchar
职位描述 post_comment varchar
薪水 salary double
办公室 office int
部门编号 depart_id int
#建表和数据准备
create table employee(
id int not null unique auto_increment,
emp_name varchar(20) not null,
sex enum('male','female') not null default 'male', #大部分是男的
age int(3) unsigned not null default 28,
hire_date date not null,
post varchar(50),
post_comment varchar(100),
salary double(15,2),
office int, #一个部门一个屋子
depart_id int
);
#查看表结构
mysql> desc employee;
+--------------+-----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+-----------------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| emp_name | varchar(20) | NO | | NULL | |
| sex | enum('male','female') | NO | | male | |
| age | int(3) unsigned | NO | | 28 | |
| hire_date | date | NO | | NULL | |
| post | varchar(50) | YES | | NULL | |
| post_comment | varchar(100) | YES | | NULL | |
| salary | double(15,2) | YES | | NULL | |
| office | int(11) | YES | | NULL | |
| depart_id | int(11) | YES | | NULL | |
+--------------+-----------------------+------+-----+---------+----------------+
#插入数据
#三个部门：教学，销售，运营
insert into employee(emp_name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','鸡汤导师',7300.33,401,1), #以下是教学部
('alex','male',78,'20150302','teacher',1000000.31,401,1),
('wupeiqi','male',81,'20130305','teacher',8300,401,1),
('yuanhao','male',73,'20140701','teacher',3500,401,1),
('liwenzhou','male',28,'20121101','teacher',2100,401,1),
('jingliyang','female',18,'20110211','teacher',9000,401,1),
('jinxin','male',18,'19000301','teacher',30000,401,1),
('成龙','male',48,'20101111','teacher',10000,401,1),
('歪歪','female',48,'20150311','sale',3000.13,402,2),#以下是销售部门
('丫丫','female',38,'20101101','sale',2000.35,402,2),
('丁丁','female',18,'20110312','sale',1000.37,402,2),
('星星','female',18,'20160513','sale',3000.29,402,2),
('格格','female',28,'20170127','sale',4000.33,402,2),
('张野','male',28,'20160311','operation',10000.13,403,3), #以下是运营部门
('程咬金','male',18,'19970312','operation',20000,403,3),
('程咬银','female',18,'20130311','operation',19000,403,3),
('程咬铜','male',18,'20150411','operation',18000,403,3),
('程咬铁','female',18,'20140512','operation',17000,403,3)
;
#ps：如果在windows系统中，插入中文字符，select的结果为空白，可以将所有字符编码统一设置成gbk
between 80 and 100 值在80到100之间
在一个模糊的范围里 between 10000 and 20000 salary 是1w-2w之间的所有人的名字
select emp_name from employee where salary between 10000 and 20000;
通配符可以是%或**_** %表示任意多字符 _表示一个字符
select * from employee where emp_name like ‘程%‘;
?
逻辑运算 - 条件的拼 (与 and) (或 or) (非 not)
select * from employee where emp_name not in (‘程咬金‘,‘程咬银‘,‘程咬铜‘);
select emp_name,salary*12 from employee where post=‘operation‘ and emp_name like ‘程%‘;
查看岗位描述为NULL的员工信息
select * from employee where post_comment is not null;
select emp_name,salary*12 from employee where post=‘teacher‘ and emp_name regexp ‘^jin.*‘
select * from employee where emp_name regexp ‘^j[a-z]{5}‘
#单独使用GROUP BY关键字分组
mysql> select post from employee group by post;
+--------------+
| post |
+--------------+
| operation |
| sale |
| teacher |
| 鸡汤导师 |
+--------------+
4 rows in set (0.02 sec)
注意：我们按照post字段分组，那么select查询的字段只能是post，想要获取组内的其他相关信息，需要借助函数
#GROUP BY关键字和GROUP_CONCAT()函数一起使用
mysql> select post,group_concat(emp_name) from employee group by post;#按照岗位分组，并查看组内成员名
+--------------+---------------------------------------------------------+
| post | group_concat(emp_name) |
+--------------+---------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| sale | 格格,星星,丁丁,丫丫,歪歪 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
| 鸡汤导师 | egon |
+--------------+---------------------------------------------------------+
4 rows in set (0.04 sec)
mysql> select post,group_concat(emp_name) as emp_members from employee group by post;
+--------------+---------------------------------------------------------+
| post | emp_members |
+--------------+---------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| sale | 格格,星星,丁丁,丫丫,歪歪 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
| 鸡汤导师 | egon |
+--------------+---------------------------------------------------------+
4 rows in set (0.00 sec)
#GROUP BY与聚合函数一起使用
select post,count(id) as count from employee group by post;#按照岗位分组，并查看每个组有多少人
+--------------+-------+
| post | count |
+--------------+-------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 鸡汤导师 | 1 |
+--------------+-------+
4 rows in set (0.02 sec)
分组会把在group by后面的这个字段，也就是post字段中的每一个不同的项都保留下来
并且把值是这一项的的所有,行归为一组,但是只显示第一个分组匹配上值的所有数据,且一般默认倒序显示,数值的默认从小到大排序.
#强调：聚合函数聚合的是组的内容，若是没有分组，则默认一组
示例：
# count(字段/*) 统计这个字段有多少项
select count(id) from employee;
+-----------+
| count(id) |
+-----------+
| 18 |#结果
+-----------+
1 row in set (0.00 sec)
select count(*) from employee where depart_id=1;
+----------+
| count(*) |
+----------+
| 8 |#结果
+----------+
1 row in set (0.00 sec)
# max(字段) 统计这个字段对应的数值的最大值(薪资)
select max(salary) from employee;
+-------------+
| max(salary) |
+-------------+
| 1000000.31 |#结果
+-------------+
1 row in set (0.03 sec)
# min(字段) 统计这个字段对应的数值的最小值(薪资)
select min(salary) from employee;
+-------------+
| min(salary) |
+-------------+
| 1000.37 |#结果
+-------------+
1 row in set (0.00 sec)
# avg(字段) 统计这个字段对应的数值的平均值(薪资)
select avg(salary) from employee;
+--------------+
| avg(salary) |
+--------------+
| 64844.568889 |#结果
+--------------+
1 row in set (0.00 sec)
# sum(字段) 统计这个字段对应的数值的和
mysql> select sum(salary) from employee;
+-------------+
| sum(salary) |
+-------------+
| 1167202.24 |#结果
+-------------+
1 row in set (0.00 sec)
select sum(salary) from employee where depart_id=3;
+-------------+
| sum(salary) |
+-------------+
| 84000.13 |#结果
+-------------+
1 row in set (0.00 sec)一 concat()函数
1、功能：将多个字符串连接成一个字符串。
2、语法：concat(str1, str2,...)
返回结果为连接参数产生的字符串，如果有任何一个参数为null，则返回值为null。
3、语法：concat(str1, seperator,str2,seperator,...)
返回结果为连接参数产生的字符串并且有分隔符，如果有任何一个参数为null，则返回值为null。
二 concat_ws()函数
1、功能：和concat()一样，将多个字符串连接成一个字符串，但是可以一次性指定分隔符（concat_ws就是concat with separator）
2、语法：concat_ws(separator, str1, str2, ...)
说明：第一个参数指定分隔符。需要注意的是分隔符不能为null，如果为null，则返回结果为null。
三 group_concat()函数
1、功能：将group by产生的同一个分组中的值连接起来，返回一个字符串结果。
2、语法：group_concat( [distinct] 要连接的字段 [order by 排序字段 asc/desc ] [separator '分隔符'] )
说明：通过使用distinct可以排除重复值；如果希望对结果中的值进行排序，可以使用order by子句；separator是一个字符串值，缺省为一个逗号。1. 查询岗位名以及岗位包含的所有员工名字
mysql> select post,group_concat(emp_name) from employee group by post;
+--------------+---------------------------------------------------------+
| post | group_concat(emp_name) |
+--------------+---------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| sale | 格格,星星,丁丁,丫丫,歪歪 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
| 鸡汤导师 | egon |
+--------------+---------------------------------------------------------+
2. 查询岗位名以及各岗位内包含的员工个数
mysql> select post,count(emp_name) from employee group by post ;
+--------------+-----------------+
| post | count(emp_name) |
+--------------+-----------------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 鸡汤导师 | 1 |
+--------------+-----------------+
3. 查询公司内男员工和女员工的个数
select sex, count(id) from employee group by sex;
+--------+-----------+
| sex | count(id) |
+--------+-----------+
| male | 10 |
| female | 8 |
+--------+-----------+
4. 查询岗位名以及各岗位的平均薪资
select post,avg(salary) from employee group by post;
+--------------+---------------+
| post | avg(salary) |
+--------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 鸡汤导师 | 7300.330000 |
+--------------+---------------+
5. 查询岗位名以及各岗位的最高薪资
select post,max(salary) from employee group by post;
+--------------+-------------+
| post | max(salary) |
+--------------+-------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 鸡汤导师 | 7300.33 |
+--------------+-------------+
6. 查询岗位名以及各岗位的最低薪资
select post,min(salary) from employee group by post;
+--------------+-------------+
| post | min(salary) |
+--------------+-------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 鸡汤导师 | 7300.33 |
+--------------+-------------+
7. 查询男员工与男员工的平均薪资，女员工与女员工的平均薪资
select sex,avg(salary) from employee group by sex;
+--------+---------------+
| sex | avg(salary) |
+--------+---------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+---------------+#HAVING与WHERE不一样的地方在于!!!!!!
1. 执行优先级从高到低：where > group by > having
2. Where 发生在分组group by之前，因而Where中可以有任意字段，但是绝对不能使用聚合函数。
3. Having发生在分组group by之后，因而Having中可以使用分组的字段，无法直接取到其他字段,可以使用聚合函数
标签：运算符 描述 单表 mes char rom 方式 员工 with
原文地址：https://www.cnblogs.com/guokaifeng/p/11179948.html
