Python进阶----pymysql模块的使用,单表查询
Python进阶----pymysql模块的使用,单表查询
一丶使用pymysql
1.下载pymysql包: pip3 install pymysql
2.编写代码
###### 增加数据
import pymysql # 导入pymysql模块
# 1. 生成conn连接对象 固定语法
conn=pymysql.Connect(host='127.0.0.1', user='root', password="123",
database='day40', port=3306,)
# 2.创建游标对象,用于操作数据库
cur=conn.cursor()
with open('test','r',encoding='utf-8') as f:
for line in f:
# 学python从开始到放弃 | alex | 人民大学出版社 | 50 | 2018 - 7 - 1
line=line.strip().split('|')
# 3 编写sql语句 %s是sql语言的占位符 和python无关
sql='insert into book(b_name,auth, press,price,p_date) values(%s,%s,%s,%s,%s)'
# 4. 执行sql语句 , execute方法,可以拼接sql语句
cur.execute(sql,line)
# 5. 增, 删, 改 数据 都需要进行提交
conn.commit()
# 6 关闭操作游标, 关闭连接
cur.close()
conn.close()
#### 查询数据
import pymysql # 导入pymysql模块
# 1. 生成conn连接对象 固定语法
conn=pymysql.Connect(host='127.0.0.1', user='root', password="123",
database='day40', port=3306,)
# 2.创建游标对象,用于操作数据库
cur=conn.cursor()
# 3. 编写sql语句
sql = 'select * from book'
# 4. 执行sql
cur.execute(sql)
# 5. 查询结果
res1 = cur.fetchone() # 查询一条 以元组的形式返回数据
res2 = cur.fetchmany(2) # 查询多条
res3 = cur.fetchall() # 查询全部
print(res1) # 控制台打印结果
print(res2)
print(res3)
# 6 关闭操作游标, 关闭连接
cur.close()
conn.close()
二丶单表查询
单标查询语法:
SELECT DISTINCT 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
关键字执行的优先级
#3## 特别重要 👇
from :找到表:from
where :拿着where指定的约束条件，去文件/表中取出一条条记录
group by :将取出的一条条记录进行分组group by，如果没有group by，则整体作为一组
select :执行select
distinct :去重
having :将分组的结果进行having过滤
order by : 将结果按条件排序：order by desc降序 acs升序
limit :限制结果的显示条数
建表:
# 创建表
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,
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 | |
+--------------+-----------------------+------+-----+---------+----------------+
#插入记录
#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','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
### 使用函数
select user(); # 获取当前用户
select database(); # 获取当前数据库
select now(); # 获取当前时间
### 简单查询
# 查询全部字段
SELECT id,emp_name,sex,age,hire_date,post,post_comment,salary,office,depart_id
FROM employee;
# 查所有
SELECT * FROM employee;
# 查询指定字段
SELECT emp_name,salary FROM employee;
### 查询去重 distinct
# 查看有几个部门
select distinct post from employee;
### 查询通过四则运算
# 查看 每个人的年薪
select emp_name, salary*12 from emplpoyee;
### 更改别名
# as
select emp_name, salary*12 AS Annual_salary from employee;
# 字段后直接跟别名
select emp_name, salary*12 Annual_salary from employee;
### 定义显示格式
# CONCAT()函数: 字段与分隔符号 以逗号间隔
select concat('姓名:',emp_name,'年薪:',salary*12) from employee;
# CONCAT_WS()函数: 第一个参数必须是分隔符,
select concat_ws(':' , emp_name, salary*12) from employee;
# 结合CASE 语句:
#语法: ( case when 条件1 then 显示内容 when 条件2 then 显示内容 else 显示内容 end )
select
(
case
when emp_name='jingliyang' then
emp_name
when emp_name='alex' then
concat(emp_name,'_BIGSB')
else
concat(emp_name,'SB')
end
) as new_name
from
employee;
#### 练习:
#1 查出所有员工的名字，薪资,格式为
<名字:egon> <薪资:3000>
# select concat('<名字:',emp_name,'>'),concat('<薪资:',salary,'>') from employee;
#2 查出所有的岗位（去掉重复）
# select distinct post from employee;
#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
# select emp_name ,salary*12 from employee;
Where查询:
### 常用的模式
# 比较运算符: > 大于, < 小于, >= 大于等于, <=小于等于 , != 不等于, <> 不等于
# between 80 and 100 : 在80 到 100 的范围内, 包含 80 和 100
# in(80,90,100) : 值是80 或者 90 或者 100
# 模糊查询
# like : % 表示任意多个字符, _表示一个字符
# 1. like 'a%' 以a开头的.
# 2. like '%a' 以a结尾的
# 3. like '_a' Xa 两个字符
# 4. like 'a_' aX 两个字符
# regexp :正则匹配
# 1. '^a' 以a开头
# 2. '\d+' 纯数字
# 3. 'a$' 以a结尾
# is 和 is not
is null : 是空
is not null : 非空
# 逻辑运算符: and与 or或 not非
where案例
# 1. 条件查询
select emp_name from employee where post='sale';
# 2. 多条件查询
select emp_name , salary from employee where port='teacher' and salary>10000;
# 3.关键字 between and
select emp_name ,salary from employee where salary beetween 10000 and 20000;
# 4.关键字 is null 判断某个字段是不是空,不能用等号
select emp_name,post_comment from employee where post_comment is null;
select emp_name,post_comment from employee where post_comment is not null;
# 判断是不是
select emp_name,post_comment from employee where post_comment='' ;
# 5.关键字IN集合查询
SELECT emp_name,salary FROM employee
WHERE salary=3000 OR salary=3500 OR salary=4000 OR salary=9000 ;
SELECT emp_name,salary FROM employee
WHERE salary IN (3000,3500,4000,9000) ;
SELECT emp_name,salary FROM employee
WHERE salary NOT IN (3000,3500,4000,9000) ;
# 6.关键字LIKE模糊查询
通配符 '%' 多个字符
# 查询eg开头
select * from employee
where emp_name like 'eg%';
通配符 '_' 单个字符
# select * from employee
where emp_name like 'al__';
# 7 . regexp 依据正则匹配数据
# 找到以jin开头的数据
select emp_name ,salary*12 from employee where emp_name regexp '^jin'
### 练习
1. 查看岗位是teacher的员工姓名、年龄
# select emp_name , age from employee where post ='teacher';
2. 查看岗位是teacher且年龄大于30岁的员工姓名、年龄
# select emp_name , age from employee where post ='teacher' and age>30;
3. 查看岗位是teacher且薪资在9000-10000范围内的员工姓名、年龄、薪资
# select emp_name , age ,salary*12 from employee where post ='teacher' and salary between 9000 and 10000;
4. 查看岗位描述不为NULL的员工信息
# select * from employee where post_comment is not null;
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
# select emp_name , age ,salary from employee where post ='teacher' and salary in (9000,10000,30000);
# select emp_name , age ,salary from employee where post ='teacher' and salary=9000 or salary=10000 or salary=30000;
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
# select emp_name , age ,salary from employee where post ='teacher' and salary not in (9000,10000,30000);
# select emp_name , age ,salary from employee where post ='teacher' and not (salary=9000 or salary=10000 or salary=30000);
7. 查看岗位是teacher且名字是jin开头的员工姓名、年薪
# select emp_name ,salary*12 from employee where post='teacher' and emp_name like 'jin%';
# select emp_name ,salary*12 from employee where post='teacher' and emp_name regexp '^jin';
GROUP BY 分组查询:
特点:
根据某个重复率比较高的字段进行的
一旦分组了就不能对具体的一条数据进行操作
group_concat():只用来做最重的显示,不能作为中间的结果操作其他数据
分组具有去重的效果
### 单独使用group by 关键字分组查询 . 每次操作都是以组的形式操作这些数据
# 按照部门进行分组,获得每个部门的名字 (有去重的效果)
select post from employee group by post;
### group by 和 group_concat()函数一起使用
# group_concat()只是用来显示内容
# 按照岗位分组,并查看组内所有成员
select post,group_concat(emp_name) from employee group by post;
### group by 和 聚合函数 一起使用
# 按照岗位分组,并查看每组有多少人
select post,count(id) as count for employee group by post;
##### 强调
1.如果我使用 unique 字段作为分组依据, 则每条记录自成一组,这样没有意义
2. 通常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
HAVING 组过滤:
特点:
对一个组进行条件筛选
优先级:
1. 优先级where > group by > having
2.where发生在分组group by之前,where可以有任意字段,where绝对不会和聚合函数一起使用.
3.having发生在分组group by之后,因而having可以使用分组的字段,单无法直接取到其他字段
## 验证 1.
mysql> select post from employee where count(salary) group by post;
ERROR 1111 (HY000): Invalid use of group function
## 验证 2.
#错误，分组后无法直接取到salary字段
mysql> select post,group_concat(emp_name) from employee group by post having salary>1000;
ERROR 1054 (42S22): Unknown column 'salary' in 'having clause'
#可以使用聚合函数获取未定义字段信息
mysql> select post,group_concat(emp_name) from employee group by post having avg(salary)>10000;
+-----------+---------------------------------------------------------+
| post | group_concat(emp_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 |
+-----------+---------------------------------------------------------+
### 练习
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
# select post, count(id),group_concat(emp_name) from employee group by post having count(id)<2;
3. 查询各岗位平均薪资大于10000的岗位名、平均工资
# select post,avg(salary) from employee group by post having avg(salary)>10000;
4. 查询各岗位平均薪资大于10000且小于20000的岗位名、平均工资
# select post,avg(salary) from employee group by post having avg(salary)>10000 and avg(salary)<20000;
# select post,avg(salary) from employee group by post having avg(salary) between 10000 and 20000;
聚合函数:
count() :统计某个字段出现的次数
max() : 某个字段的最大值
min() : 某个字段的最小值
avg() : 某个字段的平均值
sum() : 某个字段进行求和
### 如果没有进行分组, 那么这张表会作为一个整体成为一组
### 应用实例
# 统计这张表有多少条记录
select count(*) from employee;
# 统计这个表id字段有效值有多少个.(有效值 指的是非空)
select count(id) from employee;
# 最高的工资
select max(salary) from employee;
# 最低的工资
select min(salary) from employee;
# 平均工资
select avg(salary) from employee;
# 工资总和
select sum(salary) from employee;
### 练习
1. 查询岗位名以及岗位包含的所有员工名字
# select post, group_concat(emp_name) from employee group by post;
2. 查询岗位名以及各岗位内包含的员工个数
# select post, count(emp_name) from employee group by post;
3. 查询公司内男员工和女员工的个数
# select count(emp_name),sex from employee group by sex;
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 ;
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 ;
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 ;
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, max(salary) from employee group by sex ;
# 求各部门薪资大于1w的人的个数
select post,count(id) from employee where salary >10000 group by post;
ORDER BY 排序查询:
特点:
1.对单字段, 对多字段进行排序
2.默认升序 从小到大
3.desc 降序 从大到小, asc 升序 从小到大
### 按单列排序
# 升序排序工资
select * from employee order by salary;
# asc 升序
select * from employee order by salary asc;
# desc 降序
select * from employee order by salary desc;
### 按多列排序:
# 先排age 升序 ,再排 薪资 升序
select * from employee order by age , salary ;
# 先排age 降序 ,再排 薪资 升序
select * from employee order by age desc , salary ;
### 练习
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
# select * from employee order by age , hire_date desc;
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
# select post , avg(salary) from employee group by post having avg(salary)>10000 order by avg(salary);
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
# select post , avg(salary) from employee group by post having avg(salary)>10000 order by avg(salary) desc;
LIMIT限制查询:
特点:
1.limit(n,m) : n默认从0开始 , 从n+1开始, 取m条
2.与 limit n offset m : 用法一直
3.limit(n) : 取n条
4.和order by 搭配使用
应用:
1.分页
2.限制取值
## 实例
# 降序排序工资,每次取 3 条
select * from employee order by salary desc limit(3);
# 从第1条开始,即查出第一条,包含这一条并继续查询5条
select * from employee order by salary desc limit 0,5;
# 从第6条开始,即查出第6条,包含这一条并继续查询5条
select * from employee order by salary desc limit 5,5;
### 分页练习 分页显示，每页5条
mysql> select * from employee limit 0,5;
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
| id | emp_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 | NULL | 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 |
+----+-----------+------+-----+------------+-----------------------------------------+--------------+------------+--------+-----------+
mysql> select * from employee limit 5,5;
+----+------------+--------+-----+------------+---------+--------------+----------+--------+-----------+
| id | emp_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)
正则查询:
特点:
mysql可以使用正则进行查询
## 实例
# emp_name字段以al开头的数据
select * from employee where emp_name regexp '^al';
# emp_name字段以on结尾的数据
select * from employee where emp_name regexp 'on$';
# emp_name字段以al开头的数据
select * from employee where emp_name regexp '^al';
