python操作mysql数据库

2019-11-25 16:20:09

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一、数据库基本操作

1. 想允许在数据库写中文，可在创建数据库时用下面命令

create database zcl charset utf8;

2. 查看students表结构

desc students;

3. 查看创建students表结构的语句

show create table students;

4. 删除数据库

drop database zcl;

5. 创建一个新的字段

alter table students add column nal char(64);　

PS: 本人是很讨厌上面这种“简单解释+代码”的博客。其实我当时在mysql终端写了很多的实例，不过因为当时电脑运行一个看视频的软件，导致我无法Ctrl+C/V。现在懒了哈哈~~

二、python连接数据库

python3不再支持mysqldb。其替代模块是PyMySQL。本文的例子是在python3.4环境。

1. 安装pymysql模块

pip3 install pymysql

2. 连接数据库，插入数据实例

import pymysql#生成实例，连接数据库zclconn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')#生成游标，当前实例所处状态cur = conn.cursor()#插入数据reCount = cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)',('Jack','man',25,1351234,"CN"))reCount = cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)',('Mary','female',18,1341234,"USA"))conn.commit() #实例提交命令 cur.close()conn.close()print(reCount)

查看结果:

mysql> select* from students;+----+------+-----+-----+-------------+------+| id | name | sex | age | tel | nal |+----+------+-----+-----+-------------+------+| 1 | zcl | man | 22 | 15622341234 | NULL || 2 | alex | man | 30 | 15622341235 | NULL |+----+------+-----+-----+-------------+------+rows in set

3. 获取数据

import pymysqlconn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')cur = conn.cursor()reCount = cur.execute('select* from students')res = cur.fetchone() #获取一条数据res2 = cur.fetchmany(3) #获取3条数据res3 = cur.fetchall() #获取所有(元组格式)print(res)print(res2)print(res3)conn.commit()cur.close()conn.close()

输出:

(1, 'zcl', 'man', 22, '15622341234', None)((2, 'alex', 'man', 30, '15622341235', None), (5, 'Jack', 'man', 25, '1351234', 'CN'), (6, 'Mary', 'female', 18, '1341234', 'USA'))()

三、事务回滚

事务回滚是在数据写到数据库前执行的，因此事务回滚conn.rollback()要在实例提交命令conn.commit()之前。只要数据未提交就可以回滚，但回滚后ID却是自增的。请看下面的例子:

插入3条数据(注意事务回滚):

import pymysql#连接数据库zclconn=pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')#生成游标，当前实例所处状态cur=conn.cursor()#插入数据reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)', ('Jack', 'man', 25, 1351234, "CN"))reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s,%s,%s,%s,%s)', ('Jack2', 'man', 25, 1351234, "CN"))reCount=cur.execute('insert into students(name, sex, age, tel, nal) values(%s, %s, %s, %s, %s)', ('Mary', 'female', 18, 1341234, "USA"))conn.rollback() #事务回滚conn.commit() #实例提交命令 cur.close()conn.close()print(reCount)

未执行命令前与执行命令后(包含回滚操作)(注意ID号): 未执行上面代码与执行上面代码的结果是一样的!!因为事务已经回滚，故students表不会增加数据!

mysql> select* from students;+----+------+--------+-----+-------------+------+| id | name | sex | age | tel | nal |+----+------+--------+-----+-------------+------+| 1 | zcl | man | 22 | 15622341234 | NULL || 2 | alex | man | 30 | 15622341235 | NULL || 5 | Jack | man | 25 | 1351234 | CN || 6 | Mary | female | 18 | 1341234 | USA |+----+------+--------+-----+-------------+------+rows in set

执行命令后(不包含回滚操作):只需将上面第11行代码注释。

mysql> select* from students;+----+-------+--------+-----+-------------+------+| id | name | sex | age | tel | nal |+----+-------+--------+-----+-------------+------+| 1 | zcl | man | 22 | 15622341234 | NULL || 2 | alex | man | 30 | 15622341235 | NULL || 5 | Jack | man | 25 | 1351234 | CN || 6 | Mary | female | 18 | 1341234 | USA || 10 | Jack | man | 25 | 1351234 | CN || 11 | Jack2 | man | 25 | 1351234 | CN || 12 | Mary | female | 18 | 1341234 | USA |+----+-------+--------+-----+-------------+------+rows in set

总结：虽然事务回滚了，但ID还是自增了，不会因回滚而取消，但这不影响数据的一致性（底层的原理我不清楚~）

四、批量插入数据

import pymysql#连接数据库zclconn = pymysql.connect(host='127.0.0.1', user='root', passwd='root', db='zcl')#生成游标，当前实例所处状态cur = conn.cursor()li = [ ("cjy","man",18,1562234,"USA"), ("cjy2","man",18,1562235,"USA"), ("cjy3","man",18,1562235,"USA"), ("cjy4","man",18,1562235,"USA"), ("cjy5","man",18,1562235,"USA"),]#插入数据reCount = cur.executemany('insert into students(name,sex,age,tel,nal) values(%s,%s,%s,%s,%s)', li)#conn.rollback() #事务回滚conn.commit() #实例提交命令cur.close()conn.close()print(reCount)

pycharm下输出: 5

mysql终端显示:

mysql> select* from students; 　 #插入数据前+----+-------+--------+-----+-------------+------+| id | name | sex | age | tel | nal |+----+-------+--------+-----+-------------+------+| 1 | zcl | man | 22 | 15622341234 | NULL || 2 | alex | man | 30 | 15622341235 | NULL || 5 | Jack | man | 25 | 1351234 | CN || 6 | Mary | female | 18 | 1341234 | USA || 10 | Jack | man | 25 | 1351234 | CN || 11 | Jack2 | man | 25 | 1351234 | CN || 12 | Mary | female | 18 | 1341234 | USA |+----+-------+--------+-----+-------------+------+rows in setmysql> mysql> select* from students;　　　#插入数据后+----+-------+--------+-----+-------------+------+| id | name | sex | age | tel | nal |+----+-------+--------+-----+-------------+------+| 1 | zcl | man | 22 | 15622341234 | NULL || 2 | alex | man | 30 | 15622341235 | NULL || 5 | Jack | man | 25 | 1351234 | CN || 6 | Mary | female | 18 | 1341234 | USA || 10 | Jack | man | 25 | 1351234 | CN || 11 | Jack2 | man | 25 | 1351234 | CN || 12 | Mary | female | 18 | 1341234 | USA || 13 | cjy | man | 18 | 1562234 | USA || 14 | cjy2 | man | 18 | 1562235 | USA || 15 | cjy3 | man | 18 | 1562235 | USA || 16 | cjy4 | man | 18 | 1562235 | USA || 17 | cjy5 | man | 18 | 1562235 | USA |+----+-------+--------+-----+-------------+------+rows in set

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