Python学习系列（七）( 数据库编程）

一，MySQL-Python插件

Python里操作MySQL数据库，需要Python下安装访问MySQL数据库接口API包即插件，从而使得Python2.7能访问操作MySQL数据库。MySQL软件可以去官网下载：http://www.mysql.com/; MySQLdb插件下载：http://sourceforge.net/projects/mysql-python/files/latest/download

二，访问MySQL数据库

1，连接数据库mysql

基本格式：connect ([host=]'ip',[user=]'user',[passwd=]'password',[db=]'dbname')

2，数据库的基本操作

1）create创建表

 1 import MySQLdb
 2 #connect to a database 'test'
 3 conn=MySQLdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 4 cursor=conn.cursor()
 5 #create a table
 6 cursor.execute('create table 
 7 test(ID int primary key auto_increment,Name char(25))')
 8 #Closing database
 9 cursor.close()
10 conn.close()

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2）fetchall访问：

 1 import MySQLdb
 2 #connect to a database 'test'
 3 conn=MySQLdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 4 cursor=conn.cursor()
 5 #fetch datas
 6 n=cursor.execute('select * from test;')
 7 r=cursor.fetchall()
 8 print n,r
 9 #Closing database
10 cursor.close()
11 conn.close()
12 
13 >>> ================================ RESTART ================================
14 >>> 
15 3 ((4L, 'zhangbc'), (5L, 'lis08'), (6L, 'wangw'))
16 >>>

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在Mysql5.6环境下运行：

3）insert向表中插入数据：

 1 import MySQLdb
 2 #connect to a database 'test'
 3 conn=MySQLdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 4 cursor=conn.cursor()
 5 #insert data into table 'test'
 6 mysql='''insert into test(id,sname) values(4,'zhanghua')'''
 7 cursor.execute(mysql)
 8 conn.commit()#below mysql5.0 needed
 9 #fetch datas
10 n=cursor.execute('select * from test;')
11 r=cursor.fetchall()
12 print n,r
13 #Closing database
14 cursor.close()
15 conn.close()
16 
17 >>> ================================ RESTART ================================
18 >>>
19 4 ((1L, 'zhangbc'), (2L, 'lis'), (3L, 'wangw'), (4L, 'zhanghua'))

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注意：一定要写上conn.commit();事物不提交，将回滚。比较：

4）update修改表中数据：

 1 import MySQLdb
 2 #connect to a database 'test'
 3 conn=MySQLdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 4 cursor=conn.cursor()
 5 #update data of the table 'test'
 6 mysql='''update test set sname='Lisi08' where id=2'''
 7 cursor.execute(mysql)
 8 conn.commit()#below mysql5.0 needed
 9 #fetch datas
10 n=cursor.execute('select * from test;')
11 r=cursor.fetchall()
12 print n,r
13 #Closing database
14 cursor.close()
15 conn.close()
16 
17 >>> ================================ RESTART ================================
18 >>>
19 4 ((1L, 'zhangbc'), (2L, 'Lisi08'), (3L, 'wangw'), (4L, 'zhanghua'))

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5）delete删除表中数据：

 1 import MySQLdb
 2 #connect to a database 'test'
 3 conn=MySQLdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 4 cursor=conn.cursor()
 5 #delete data of the table 'test'
 6 mysql='''delete from test where id=4'''
 7 cursor.execute(mysql)
 8 conn.commit()#below mysql5.0 needed
 9 #fetch datas
10 n=cursor.execute('select * from test;')
11 r=cursor.fetchall()
12 print n,r
13 #Closing database
14 cursor.close()
15 conn.close()
16 
17 >>> ================================ RESTART ================================
18 >>>
19 3 ((1L, 'zhangbc'), (2L, 'Lisi08'), (3L, 'wangw'))

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6）关于select及其遍历：

i）使用元组tuple与fetchone结合

 1 import MySQLdb
 2 #connect to a database 'test'
 3 conn=MySQLdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 4 cursor=conn.cursor()
 5 #fetch datas
 6 cursor.execute('select * from test;')
 7 #获得结果集的记录
 8 numrows=int(cursor.rowcount)
 9 #循环，取行数据
10 for i in range(numrows):
11     row=cursor.fetchone()
12     print row[0],row[1]
13 #Closing database
14 cursor.close()
15 conn.close()
16 
17 >>> ================================ RESTART ================================
18 >>> 
19 4 zhangbc
20 5 lis08
21 6 wangw

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ii）使用字典cursor

 1 #-*- coding:UTF-8 -*-
 2 import MySQLdb as mdb
 3 #connect to a database 'test'
 4 conn=mdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 5 with conn:
 6     #获取连接上的字典cursor，每一个cursor其实都是cursor的子类
 7     cur=conn.cursor(mdb.cursors.DictCursor)
 8 #fetch datas
 9 cur.execute('select * from test;')
10 #获得结果集
11 rows=cur.fetchall()
12 #循环，取行数据
13 for row in rows:
14     print '%s %s'%(row['ID'],row['Name'])
15 #Closing database
16 cur.close()
17 conn.close()
18 
19 >>> ================================ RESTART ================================
20 >>> 
21 4 zhangbc
22 5 lis08
23 6 wangw

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iii）获取单个表的字段名及其信息

 1 #-*- coding:UTF-8 -*-
 2 import MySQLdb as mdb
 3 #connect to a database 'test'
 4 conn=mdb.connect(host='localhost',user='root',passwd='zbc123',db='test')
 5 with conn:
 6     #获取连接上的字典cursor，每一个cursor其实都是cursor的子类
 7     cur=conn.cursor()
 8 #fetch datas
 9 cur.execute('select * from test;')
10 #获得结果集
11 rows=cur.fetchall()
12 #获得链接对象的描述信息
13 desc=cur.description
14 print 'cur.description:',desc
15 #打印表头
16 print '%2s %3s'%(desc[0][0],desc[1][0])
17 #循环，取行数据
18 for row in rows:
19     print '%2s %3s'%row
20 #Closing database
21 cur.close()
22 conn.close()
23 
24 >>> ================================ RESTART ================================
25 >>> 
26 cur.description: (('ID', 3, 1, 11, 11, 0, 0), ('Name', 254, 7, 25, 25, 0, 1))
27 ID Name
28  4 zhangbc
29  5 lis08
30  6 wangw

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三，小结

本文主要介绍了Python下如何访问并操数据库的基本知识，如：如何连接数据库，如何执行执行SQL语句等等。