文章目录
- mysql单表查询
- 一、单表查询语法
- 二、 关键字执行的优先级(重点)
- 三、简单查询
- 四、单表查询
- 1、select（筛选列语句）
- 1）select 查询操作
- 2）distinct 去重操作
- 3）四则运算
- 4）concat和concat_ws(自定义显示的格式)
- 5）case end 语句
- 6）select的相关总结
- 2、 where （筛选行语句）
- 1） where 概述
- 2）where 查询的使用
- 3）案列：
- 3、 group by(分组查询)
- 1）group by概述
- 2）group by 查询的使用
- 3) group by
- 4、 聚合函数 （count、max、min、avg、sum ）
- 1）常用的聚合函数
- 2）聚合函数的使用
- 3) 案列：
- 5、 having (过滤条件)
- 1）having与where的关系
- 2）having 与where对比
- 3）案列：
- 6、 order by （排序）
- 1）asc与desc（升序与降序）
- 2）排序方式
- 3）案列：
- 7、limit（限制查询记录；分页）
- 1）limit的使用
- 2）案列：
- 8、regexp(正则查询)
- 1）regexp使用
- 2）案列：
mysql单表查询
一、单表查询语法
#基础格式：
SELECT 字段1,字段2... FROM 表名
WHERE 条件
GROUP BY field
HAVING 筛选
ORDER BY field
LIMIT 限制条数 二、 关键字执行的优先级(重点)
【select查询语句执行顺序详解URL】
基本流程：
首先执行命令:select —>找到表:from —>拿着指定的约束条件，去文件/表中取出一条条记录：where —>将取出的一条条记录进行分组，如果没有group by，则整体作为一组：group by —>将分组的结果进行过滤：having —>然后进行去重：distinct —>将结果按条件进行排序：order by —> 最后输出限制结果的显示条数:limit
# ！！！重点：(关键字的执行优先级)
1:from #找到表
2:where #使用where指定的条件,去表中取出一条条记录
3:group by #将取出的数据进行分组,如果没有指定,则整体作为一组
4:having #将分组的结果按照having指定的条件进行过滤
5:select #指定select查询
6:distinct #去重
7:order by #将查询的结果按照order by指定的字段进行排序
8:limit #限制结果的显示数量 三、简单查询
#准备表和记录
company.employee
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
#创建表
create table employee(
id int not null unique auto_increment,
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 |
| 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 | |
+--------------+-----------------------+------+-----+---------+----------------+
#插入记录
#三个部门：教学，销售，运营
insert into employee(name,sex,age,hire_date,post,salary,office,depart_id) values
('egon','male',18,'20170301','老男孩驻沙河办事处外交大使',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 ###########################(简单查询)###########################
SELECT id,name,sex,age,hire_date,post,post_comment,salary,office,depart_id
FROM employee;
SELECT * FROM employee;
SELECT name,salary FROM employee;
#避免重复DISTINCT(去重)
SELECT DISTINCT post FROM employee;
#通过四则运算查询（运算）
SELECT name, salary*12 FROM employee;
SELECT name, salary*12 AS Annual_salary FROM employee;
SELECT name, salary*12 Annual_salary FROM employee;
#定义显示格式
CONCAT() #函数用于连接字符串
SELECT CONCAT('姓名: ',name,' 年薪: ', salary*12) AS Annual_salary
FROM employee;
CONCAT_WS() #第一个参数为分隔符
SELECT CONCAT_WS(':',name,salary*12) AS Annual_salary
FROM employee;
#结合CASE语句：
SELECT
(
CASE
WHEN NAME = 'egon' THEN
NAME
WHEN NAME = 'alex' THEN
CONCAT(name,'_BIGSB')
ELSE
concat(NAME, 'SB')
END
) as new_name
FROM
emp; ###########(小练习）
1)查出所有员工的名字，薪资,格式为:
<名字:egon> <薪资:3000>
2)查出所有的岗位（去掉重复）
3)查出所有员工名字，以及他们的年薪,年薪的字段名为annual_year
#查询以上条件（code编写）
select concat('<名字:',name,'> ','<薪资:',salary,'>') from employee;
select distinct depart_id from employee;
select name,salary*12 annual_salary from employee; 四、单表查询
1、select（筛选列语句）
1）select 查询操作
#注意:所有select 查询后面右加括号的方法,比如,select user()这种带括号的都是Mysql的内置方法,select本身就是查询操作,from只是说明从哪查
select * from 表名; #查询表中所有的数据 *代表所有
select 字段名 from 表名; #查询表中某一个字段的数据
select 字段名,字段名,字段名 from 表名; #查询表中多个字段的数据
select database(); #查询返回当前操作的数据库
select user(); #查询当前登陆的用户
select now; #查询返回当前的时间 2）distinct 去重操作
'''
select dictinct 字段名 from 表名;#对查出来的字段数据进行去重
select distinct 字段名,字段名 from 表名;#对多个字段查询的数据进行联合去重 3）四则运算
#使用select 查询某个字段的数据的时候,对数值类型的字段数据,可以进行四则运算,四则运算包括加减乘除等操作
select 字段名*12 from 表名; #对查询出来的数据乘以12,返回结果,>>字段名要是数值类型 4）concat和concat_ws(自定义显示的格式)
concat (字符串拼接)
concat_ws (指定分割符进行拼接)
#concat内置函数可以对查询出来的字段数据进行字符串拼接
select concat('姓名:',name) from 表名; #对查询出来的姓名字段的数据前面都加上一个字符串姓名,能够友好的显示查询出来的数据的意思,其实就是字符串拼接
select concat(name,':',salary)as info from 表名; #concat还可以将两个字段的数据拼接,,产生一个新的字段数据显示出来,as是个这个字段重命名
concat_ws()函数也只是字符串拼接,不过concat_ws的凭借方式是类似与python join拼接的方式,就是以某个元素对多个字段的数据进行拼接
select concat_ws('_','姓名:',name,'性别:',sex)as info from 表名; 5）case end 语句
case end 语句对查询出来的每一个数据进行加工和显示
#case语句的作用:
对表中数据进行查询时,对于查询出来的语句进行进一步的加工,并且显示出来,case end语句有点像python里的if语句,不过sql的case语句需要表明开始和结束,case代表开始,end代表束.when代表的就是if条件,else就是其他,当有多个when的时候,从第二个when开始就代表的类似于elif的意思,知道了解就好----->
select(
case
when name='田少岗' concat(name,'逗比')
when name='田彩' concat(name,'女神')
else
concat(name,'边玩去')
end
)as now_name from 表名; 6）select的相关总结
1>#可以查一个,多个,*所有调用函数： now(),database(),concat(),concat_ws()
2>#可以四则运算
3>#可以去重 distinct
4>#可以使用case end 条件判断语句 2、 where （筛选行语句）
1） where 概述
1:#范围查询
#< > >= <= != <>代表不等于和!=是一个意思
select age from 表名 where age <100 and age>20;(多条件查询)
#between 1 and 10 找寻1到10之间的
select age from 表名 where between 1 and 100; >>注意包含1和100
#in (1,2,3,4) 多选一
select age from 表名 where age in (10,20,30,40);
#将age=10和age=20的都能取出来
select age from 表名 where age=10 or age=20;
2:#模糊查询
#like
like的表现形式是:'%a'查询以a结尾的,'a%'查询以a开始的,'%a%'查询包含a的
select name from 表名 where name like '田%';>>> #查询出姓田的所有人
like还有一种形式,'_a','a_','a__'一个划线代表一个字符,%代表的是任意长度
select name from 表名 where name 'like '田_';>>> #查询出以田开头的两个字的姓名
(pattern可以是%或_
%表示任意多字符
_表示一个字符)
#regexp 可以使用正则匹配(记一下正则表达式)
3:#is is not
is null is not null #一般用来判断是不是空
4:#逻辑运算: 2）where 查询的使用
#1:单条件查询
SELECT name FROM employee
WHERE post='sale';
#2:多条件查询
SELECT name,salary FROM employee
WHERE post='teacher' AND salary>10000;
#3:关键字BETWEEN AND
SELECT name,salary FROM employee
WHERE salary BETWEEN 10000 AND 20000;
SELECT name,salary FROM employee
WHERE salary NOT BETWEEN 10000 AND 20000;
#4:关键字IS NULL(判断某个字段是否为NULL不能用等号，需要用IS)
SELECT name,post_comment FROM employee
WHERE post_comment IS NULL;
SELECT name,post_comment FROM employee
WHERE post_comment IS NOT NULL;
SELECT name,post_comment FROM employee
WHERE post_comment=''; 注意''是空字符串，不是null
ps：
执行
update employee set post_comment='' where id=2;
再用上条查看，就会有结果了
#5:关键字IN集合查询
SELECT name,salary FROM employee
WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
SELECT name,salary FROM employee
WHERE salary IN (3000,3500,4000,9000) ;
SELECT name,salary FROM employee
WHERE salary NOT IN (3000,3500,4000,9000) ;
#6:关键字LIKE模糊查询
通配符’%’
SELECT * FROM employee
WHERE name LIKE 'eg%';
通配符’_’
SELECT * FROM employee
WHERE name LIKE 'al__'; 3）案列：
#示列：
1. 查看岗位是teacher的员工姓名、年龄
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
3. 查看岗位是teacher且薪资在9000-1000范围内的员工姓名、年龄、薪资
4. 查看岗位描述不为NULL的员工信息
5. 查看岗位是teacher且薪资是10000或9000或30000的员工姓名、年龄、薪资
6. 查看岗位是teacher且薪资不是10000或9000或30000的员工姓名、年龄、薪资
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪
#where使用
1》select name,age from employee where post = 'teacher';
2》select name,age from employee where post='teacher' and age > 30;
3》select name,age,salary from employee where post='teacher' and salary between 9000 and 10000;
4》select * from employee where post_comment is not null;
5》select name,age,salary from employee where post='teacher' and salary in (10000,9000,30000);
6》select name,age,salary from employee where post='teacher' and salary not in (10000,9000,30000);
7》select name,salary*12 from employee where post='teacher' and name like 'jin%'; 3、 group by(分组查询)
1）group by概述
#1、首先明确一点：分组发生在where之后，即分组是基于where之后得到的记录而进行的
#2、分组指的是：将所有记录按照某个相同字段进行归类，比如针对员工信息表的职位分组，或者按照性别进行分组等
#3、为何要分组呢？
取每个部门的最高工资
取每个部门的员工数
取男人数和女人数
小窍门：‘每’这个字后面的字段，就是我们分组的依据
#4、大前提： group by：可以对某个字段的值进行分组,这个字段有多少种值就分多少组,group by还有一个特性就是去重,一旦使用group by对数据分组了,就不能对某一条数据进行操作,永远都是这一组数据
group_concat()函数(只用来做最终的显示,不做中间数据的操作)可以显示当前这一组的所有信息,拼在一起显示
select post,group_concat(name),count(id) from employee group by post having count(id) < 2;
'''
###了解即可
mysql> set global sql_mode='STRICT_TRANS_TABLES,ONLY_FULL_GROUP_BY'; 2）group by 查询的使用
############！！！SQL_MODE设置！！！
#查看MySQL 5.7默认的sql_mode如下：
mysql> select @@global.sql_mode;
ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION
#注意！！！
ONLY_FULL_GROUP_BY的语义就是确定select target list中的所有列的值都是明确语义，简单的说来，在ONLY_FULL_GROUP_BY模式下，target list中的值要么是来自于聚集函数的结果，要么是来自于group by list中的表达式的值。
#设置sql_mole如下操作(我们可以去掉ONLY_FULL_GROUP_BY模式)：
mysql> set global sql_mode='STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,NO_ZERO_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'; mysql> select @@global.sql_mode;
+-------------------+
| @@global.sql_mode |
+-------------------+
| |
+-------------------+
1 row in set (0.00 sec)
mysql> select * from emp group by post;
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外交大使 | NULL | 7300.33 | 401 | 1 |
+----+------+--------+-----+------------+----------------------------+--------------+------------+--------+-----------+
4 rows in set (0.00 sec)
#由于没有设置ONLY_FULL_GROUP_BY,于是也可以有结果，默认都是组内的第一条记录，但其实这是没有意义的
mysql> set global sql_mode='ONLY_FULL_GROUP_BY';
Query OK, 0 rows affected (0.00 sec)
mysql> quit #设置成功后，一定要退出，然后重新登录方可生效
Bye
mysql> use db1;
Database changed
mysql> select * from emp group by post; #报错
ERROR 1055 (42000): 'db1.emp.id' isn't in GROUP BY
mysql> select post,count(id) from emp group by post; #只能查看分组依据和使用聚合函数
+----------------------------+-----------+
| post | count(id) |
+----------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+----------------------------+-----------+
4 rows in set (0.00 sec) 3) group by
如果我们用unique的字段作为分组的依据，则每一条记录自成一组，这种分组没有意义,多条记录之间的某个字段值相同，该字段通常用来作为分组的依据
#单独使用GROUP BY关键字分组
SELECT post FROM employee GROUP BY post;
#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
SELECT post,GROUP_CONCAT(name) FROM employee GROUP BY post; #按照岗位分组，并查看组内成员名
SELECT post,GROUP_CONCAT(name) as emp_members FROM employee GROUP BY post;
#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 4、 聚合函数 （count、max、min、avg、sum ）
分组之后:select只能看到分组字段以及聚合的结果
1）常用的聚合函数
1:#count 计数
2:#max 求最大值
3:#avg 求平均值
4:#min 求最小值
5:#sum 求和 2）聚合函数的使用
#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：
SELECT COUNT(*) FROM employee;
SELECT COUNT(*) FROM employee WHERE depart_id=1;
SELECT MAX(salary) FROM employee;
SELECT MIN(salary) FROM employee;
SELECT AVG(salary) FROM employee;
SELECT SUM(salary) FROM employee;
SELECT SUM(salary) FROM employee WHERE depart_id=3; 3) 案列：
#示列：
1》查询岗位名以及岗位包含的所有员工名字
2》查询岗位名以及各岗位内包含的员工个数
3》查询公司内男员工和女员工的个数
4》查询岗位名以及各岗位的平均薪资
5》查询岗位名以及各岗位的最高薪资
6》查询岗位名以及各岗位的最低薪资
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
8》查询出每个部门的员工数
9》查询男人数与女人数
10》查询年龄在20岁以上的男人数与女人数
11》查询每个部门20岁以上人的平均薪资
12》查询每个部门的平均薪资及最大薪资最小年龄和年龄的和
13》查询每个部门的员工及年龄
#聚合函数的使用：
#题目1:分组
mysql> select post,group_concat(name) from employee group by post;
+-----------------------------------------+---------------------------------------------------------+
| post | group_concat(name) |
+-----------------------------------------+---------------------------------------------------------+
| operation | 张野,程咬金,程咬银,程咬铜,程咬铁 |
| sale | 歪歪,丫丫,丁丁,星星,格格 |
| teacher | alex,wupeiqi,yuanhao,liwenzhou,jingliyang,jinxin,成龙 |
| 老男孩驻沙河办事处外交大使 | egon |
+-----------------------------------------+---------------------------------------------------------+
#题目2：
mysql> select post,count(id) from employee group by post;
+-----------------------------------------+-----------+
| post | count(id) |
+-----------------------------------------+-----------+
| operation | 5 |
| sale | 5 |
| teacher | 7 |
| 老男孩驻沙河办事处外交大使 | 1 |
+-----------------------------------------+-----------+
#题目3：
mysql> select sex,count(id) from employee group by sex;
+--------+-----------+
| sex | count(id) |
+--------+-----------+
| male | 10 |
| female | 8 |
+--------+-----------+
#题目4：
mysql> select post,avg(salary) from employee group by post;
+-----------------------------------------+---------------+
| post | avg(salary) |
+-----------------------------------------+---------------+
| operation | 16800.026000 |
| sale | 2600.294000 |
| teacher | 151842.901429 |
| 老男孩驻沙河办事处外交大使 | 7300.330000 |
+-----------------------------------------+---------------+
#题目5
mysql> select post,max(salary) from employee group by post;
+-----------------------------------------+-------------+
| post | max(salary) |
+-----------------------------------------+-------------+
| operation | 20000.00 |
| sale | 4000.33 |
| teacher | 1000000.31 |
| 老男孩驻沙河办事处外交大使 | 7300.33 |
+-----------------------------------------+-------------+
#题目6
mysql> select post,min(salary) from employee group by post;
+-----------------------------------------+-------------+
| post | min(salary) |
+-----------------------------------------+-------------+
| operation | 10000.13 |
| sale | 1000.37 |
| teacher | 2100.00 |
| 老男孩驻沙河办事处外交大使 | 7300.33 |
+-----------------------------------------+-------------+
#题目七
mysql> select sex,avg(salary) from employee group by sex;
+--------+---------------+
| sex | avg(salary) |
+--------+---------------+
| male | 110920.077000 |
| female | 7250.183750 |
+--------+---------------+
#题目八
mysql> select post,count(id) from employee group by post;
#题目九
mysql> select sex,count(id) from employee group by sex;
#题目十
mysql> select sex,count(id) from employee where age > 20 group by sex;
#题十一
mysql> select post,avg(salary) from employee where age > 20 group by post;
#题十二
mysql> select post,avg(salary),max(salary),min(age),count(id),sum(age) from employee group by post;
#题十三
mysql> select post,group_concat(name,":",age) from employee group by post;
+-----------------------------------------+------------------------------------------------------------------------------+
| post | group_concat(name,":",age) |
+-----------------------------------------+------------------------------------------------------------------------------+
| operation | 程咬铁:18,程咬铜:18,程咬银:18,程咬金:18,张野:28 |
| sale | 格格:28,星星:18,丁丁:18,丫丫:38,歪歪:48 |
| teacher | 成龙:48,jinxin:18,jingliyang:18,liwenzhou:28,yuanhao:73,wupeiqi:81,alex:78 |
| 老男孩驻沙河办事处外交大使 | egon:18 |
+-----------------------------------------+------------------------------------------------------------------------------+
4 rows in set (0.00 sec) 5、 having (过滤条件)
having是针对一个组做的过滤条件,是放在group by 后面执行的,他的意思和where是一样的,where group 和 having的执行顺序是:(where—>group by—>having)having一般都是和having一起用的
#示列：
select post,group_concat(name),count(id) from employee group by post having count(id) < 2; 1）having与where的关系
#having与where的之间的不同！！！
！！！执行优先级从高到低：where > group by > 2）having 与where对比
sql_mode:简而言之就是：它定义了你MySQL应该支持的sql语法，对数据的校验等等
#select @@sql_mode:使用该命令我们可以查看我们当前数据库的sql_mode
mysql> select @@sql_mode;
+--------------------+
| @@sql_mode |
+--------------------+
| ONLY_FULL_GROUP_BY |
+--------------------+
1 row in set (0.00 sec)
mysql> select * from emp where salary > 100000;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec)
mysql> select * from emp having salary > 100000;
ERROR 1463 (42000): Non-grouping field 'salary' is used in HAVING clause
mysql> select post,group_concat(name) from emp group by post having salary > 10000; #错误，分组后无法直接取到salary字段
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
mysql> select post,group_concat(name) from emp group by post having avg(salary) > 10000;
+-----------+-------------------------------------------------------+
| post | group_concat(name) |
+-----------+-------------------------------------------------------+
| operation | 程咬铁,程咬铜,程咬银,程咬金,张野 |
| teacher | 成龙,jinxin,jingliyang,liwenzhou,yuanhao,wupeiqi,alex |
+-----------+-------------------------------------------------------+
2 rows in set (0.00 sec) 3）案列：
#示列：
1》查询各岗位内包含的员工个数小于2的岗位名、岗位内包含员工名字、个数
2》查询各岗位平均薪资大于10000的岗位名、平均工资
3》查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资
4》查询出平均薪资在10000以上的部门
5》查出部门内男员工平均工资在3000以上的部门
#题1：
mysql> select post,group_concat(name),count(id) from employee group by post having count(id) < 2;
+-----------------------------------------+--------------------+-----------+
| post | group_concat(name) | count(id) |
+-----------------------------------------+--------------------+-----------+
| 老男孩驻沙河办事处外交大使 | egon | 1 |
+-----------------------------------------+--------------------+-----------+
#题目2：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+
#题目3：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 and avg(salary) <20000;
+-----------+--------------+
| post | avg(salary) |
+-----------+--------------+
| operation | 16800.026000 |
+-----------+--------------+
#题目4：
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+
2 rows in set (0.00 sec)
#题目5:
mysql> select post,avg(salary) from employee where sex="male" group by post
having avg(salary) > 3000;
+-----------------------------------------+---------------+
| post | avg(salary) |
+-----------------------------------------+---------------+
| operation | 16000.043333 |
| teacher | 175650.051667 |
| 老男孩驻沙河办事处外交大使 | 7300.330000 |
+-----------------------------------------+---------------+
3 rows in set (0.00 sec) 6、 order by （排序）
1）asc与desc（升序与降序）
; #默认不写，就是升序排列
SELECT * FROM employee ORDER BY salary ASC; #升序
SELECT * FROM employee ORDER BY salary DESC; #降序 2）排序方式
#按单列排序
SELECT * FROM employee ORDER BY salary;
SELECT * FROM employee ORDER BY salary ASC;
SELECT * FROM employee ORDER BY salary DESC;
#按多列排序:先按照age排序，如果年纪相同，则按照薪资排序
SELECT * from employee
ORDER BY age,
salary DESC; 3）案列：
#示列：
1》查询所有员工信息，先按照age升序排序，如果age相同则按照hire_date降序排序
2》查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资升序排列
3》查询各岗位平均薪资大于10000的岗位名、平均工资,结果按平均薪资降序排列
4》查询所有员工信息，按照年龄进行升序排列
5》查询所有员工信息，按照年龄进行降序排列
6》查询每个部门薪资大于3000的平均薪资，结果按升序排列
7》查询所有的员工的年龄按升序排列，id按降序排列
#题目1
mysql> select * from employee ORDER BY age asc,hire_date desc;
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外交大使 | NULL | 7300.33 | 401 | 1 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 17 | 程咬铜 | male | 18 | 2015-04-11 | operation | NULL | 18000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
| 16 | 程咬银 | female | 18 | 2013-03-11 | operation | NULL | 19000.00 | 403 | 3 |
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
+----+------------+--------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
18 rows in set (0.00 sec)
#题目2
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) asc;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| operation | 16800.026000 |
| teacher | 151842.901429 |
+-----------+---------------+
#题目3
mysql> select post,avg(salary) from employee group by post having avg(salary) > 10000 order by avg(salary) desc;
+-----------+---------------+
| post | avg(salary) |
+-----------+---------------+
| teacher | 151842.901429 |
| operation | 16800.026000 |
+-----------+---------------+
#题目4：
mysql> select * from employee order by age asc;
#题目5：
mysql> select * from employee order by age desc;
#题目6：
mysql> select post,avg(salary) from employee where sex="male" group by post
having avg(salary) > 3000
order by avg(salary);
#题目7：
mysql> select * from employee order by age asc,id desc; 7、limit（限制查询记录；分页）
1）limit的使用
#默认初始位置为0,从第一条开始顺序取出三条
SELECT * FROM employee ORDER BY salary DESC LIMIT 3; #排序后限制显示的行数
#从第0开始，即先查询出第一条，然后包含这一条在内往后查5条
SELECT * FROM employee ORDER BY salary DESC
LIMIT 0,5; #排序后指定显示的行数
##从第5开始，即先查询出第6条，然后包含这一条在内往后查5条
SELECT * FROM employee ORDER BY salary DESC
LIMIT 5,5; 2）案列：
1》分页显示，每页5条
#从第一条开始，每页显示5条
mysql> select * from employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| 1 | egon | male | 18 | 2017-03-01 | 老男孩驻沙河办事处外交大使 | NULL | 7300.33 | 401 | 1 |
| 2 | alex | male | 78 | 2015-03-02 | teacher | | 1000000.31 | 401 | 1 |
| 3 | wupeiqi | male | 81 | 2013-03-05 | teacher | NULL | 8300.00 | 401 | 1 |
| 4 | yuanhao | male | 73 | 2014-07-01 | teacher | NULL | 3500.00 | 401 | 1 |
| 5 | liwenzhou | male | 28 | 2012-11-01 | teacher | NULL | 2100.00 | 401 | 1 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
5 rows in set (0.00 sec)
#从第5条开始，每页显示5条
mysql> select * from employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------------+--------+-----+-------+---------+--------------+----------+--------+-----------+
| 6 | jingliyang | female | 18 | 2011-02-11 | teacher | NULL | 9000.00 | 401 | 1 |
| 7 | jinxin | male | 18 | 1900-03-01 | teacher | NULL | 30000.00 | 401 | 1 |
| 8 | 成龙 | male | 48 | 2010-11-11 | teacher | NULL | 10000.00 | 401 | 1 |
| 9 | 歪歪 | female | 48 | 2015-03-11 | sale | NULL | 3000.13 | 402 | 2 |
| 10 | 丫丫 | female | 38 | 2010-11-01 | sale | NULL | 2000.35 | 402 | 2 |
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)
#从第10条开始，每页显示5条
mysql> select * from employee limit 10,5;
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 11 | 丁丁 | female | 18 | 2011-03-12 | sale | NULL | 1000.37 | 402 | 2 |
| 12 | 星星 | female | 18 | 2016-05-13 | sale | NULL | 3000.29 | 402 | 2 |
| 13 | 格格 | female | 28 | 2017-01-27 | sale | NULL | 4000.33 | 402 | 2 |
| 14 | 张野 | male | 28 | 2016-03-11 | operation | NULL | 10000.13 | 403 | 3 |
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
5 rows in set (0.00 sec)
#使用limit取出薪资最高的员工
mysql> select * from employee order by salary desc limit 1;
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
| 2 | alex | male | 78 | 2015-03-02 | teacher | NULL | 1000000.31 | 401 | 1 |
+----+------+------+-----+------------+---------+--------------+------------+--------+-----------+
1 row in set (0.00 sec) 8、regexp(正则查询)
1）regexp使用
#查询name里以ale开头的名字
SELECT * FROM employee WHERE name REGEXP '^ale';
#查询name里以xin结尾的名字
select * from employee where name regexp "xin$";
#查询name里包含两个mm的名字
SELECT * FROM employee WHERE name REGEXP 'm{2}';
小结：对字符串匹配的方式
WHERE name = 'egon';
WHERE name LIKE 'yua%';
WHERE name REGEXP 'on$'; 2）案列：
1》查看所有员工中名字是jin开头，n或者g结果的员工信息
2》查询所有员工名字是程开头的，金铁结尾的员工信息
#使用regexp查询
mysql> select * from employee where name regexp '^jin.*[gn]$';
mysql> select * from employee where name regexp "^程.*[金铁]$";
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| id | name | sex | age | hire_date | post | post_comment | salary | office | depart_id |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
| 15 | 程咬金 | male | 18 | 1997-03-12 | operation | NULL | 20000.00 | 403 | 3 |
| 18 | 程咬铁 | female | 18 | 2014-05-12 | operation | NULL | 17000.00 | 403 | 3 |
+----+-----------+--------+-----+------------+-----------+--------------+----------+--------+-----------+
2 rows in set (0.00 sec) ![mysql使用source命令导入.sql文件[图]](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACwAAAAAAQABAAACAkQBADs=)