Python SQLite

在本章中，你将学习如何在Python程序中使用SQLite。

安装

可以使用sqlite3模块将SQLite集成到Python中，该模块由Gerhard Haring编写。它提供了一个符合PEP 249描述的DB-API 2.0规范的SQL接口。你不需要单独安装此模块，因为它从Python版本2.5.x开始默认随附。

要使用sqlite3模块，必须首先创建一个表示数据库的连接对象，然后可选地创建一个游标对象，该游标对象将帮助你执行所有的SQL语句。

Python sqlite3模块API

以下是重要的sqlite3模块例程，它们可以满足你在Python程序中与SQLite数据库一起工作的要求。如果你正在寻找一个更复杂的应用程序，那么可以查阅Python sqlite3模块的官方文档。

连接到数据库

以下Python代码展示了如何连接到一个已经存在的数据库。如果数据库不存在，则会被创建，最后将返回一个数据库对象。

#!/usr/bin/python

import sqlite3

conn = sqlite3.connect('test.db')

print "Opened database successfully";

在这里，你也可以使用特殊名称 :memory: 来创建一个位于RAM中的数据库。现在，让我们运行上述程序在当前目录中创建我们的数据库 test.db 。你可以根据需要改变路径。将上述代码保存在sqlite.py文件中并按照下面所示执行它。如果成功创建数据库，则会显示以下消息。

$chmod +x sqlite.py
$./sqlite.py
Open database successfully

创建表

以下Python程序将用于在之前创建的数据库中创建一个表。

#!/usr/bin/python

import sqlite3

conn = sqlite3.connect('test.db')
print "Opened database successfully";

conn.execute('''CREATE TABLE COMPANY
         (ID INT PRIMARY KEY     NOT NULL,
         NAME           TEXT    NOT NULL,
         AGE            INT     NOT NULL,
         ADDRESS        CHAR(50),
         SALARY         REAL);''')
print "Table created successfully";

conn.close()

当上述程序被执行时，它将在 test.db 中创建 COMPANY 表，并显示以下消息：

Opened database successfully
Table created successfully

插入操作

以下Python程序显示了如何在上面示例中创建的COMPANY表中创建记录。

#!/usr/bin/python

import sqlite3

conn = sqlite3.connect('test.db')
print "Opened database successfully";

conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \
      VALUES (1, 'Paul', 32, 'California', 20000.00 )");

conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \
      VALUES (2, 'Allen', 25, 'Texas', 15000.00 )");

conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \
      VALUES (3, 'Teddy', 23, 'Norway', 20000.00 )");

conn.execute("INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) \
      VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 )");

conn.commit()
print "Records created successfully";
conn.close()

当执行上面的程序时，它将在COMPANY表中创建给定的记录，并显示以下两行 –

Opened database successfully
Records created successfully

SELECT 操作

下面的 Python 程序演示了如何从上面的示例中创建的 COMPANY 表中获取和显示记录。

#!/usr/bin/python

import sqlite3

conn = sqlite3.connect('test.db')
print "Opened database successfully";

cursor = conn.execute("SELECT id, name, address, salary from COMPANY")
for row in cursor:
   print "ID = ", row[0]
   print "NAME = ", row[1]
   print "ADDRESS = ", row[2]
   print "SALARY = ", row[3], "\n"

print "Operation done successfully";
conn.close()

当执行上述程序时，它将产生以下结果。

Opened database successfully
ID = 1
NAME = Paul
ADDRESS = California
SALARY = 20000.0

ID = 2
NAME = Allen
ADDRESS = Texas
SALARY = 15000.0

ID = 3
NAME = Teddy
ADDRESS = Norway
SALARY = 20000.0

ID = 4
NAME = Mark
ADDRESS = Rich-Mond
SALARY = 65000.0

Operation done successfully

更新操作

下面的Python代码展示了如何使用UPDATE语句更新任意记录，并从COMPANY表中获取和显示更新后的记录。

#!/usr/bin/python

import sqlite3

conn = sqlite3.connect('test.db')
print "Opened database successfully";

conn.execute("UPDATE COMPANY set SALARY = 25000.00 where ID = 1")
conn.commit()
print "Total number of rows updated :", conn.total_changes

cursor = conn.execute("SELECT id, name, address, salary from COMPANY")
for row in cursor:
   print "ID = ", row[0]
   print "NAME = ", row[1]
   print "ADDRESS = ", row[2]
   print "SALARY = ", row[3], "\n"

print "Operation done successfully";
conn.close()

当上述程序被执行时，它将产生以下结果。

Opened database successfully
Total number of rows updated : 1
ID = 1
NAME = Paul
ADDRESS = California
SALARY = 25000.0

ID = 2
NAME = Allen
ADDRESS = Texas
SALARY = 15000.0

ID = 3
NAME = Teddy
ADDRESS = Norway
SALARY = 20000.0

ID = 4
NAME = Mark
ADDRESS = Rich-Mond
SALARY = 65000.0

Operation done successfully

删除操作

以下Python代码展示了如何使用DELETE语句删除任意记录，然后从COMPANY表中获取并显示剩余的记录。

#!/usr/bin/python

import sqlite3

conn = sqlite3.connect('test.db')
print "Opened database successfully";

conn.execute("DELETE from COMPANY where ID = 2;")
conn.commit()
print "Total number of rows deleted :", conn.total_changes

cursor = conn.execute("SELECT id, name, address, salary from COMPANY")
for row in cursor:
   print "ID = ", row[0]
   print "NAME = ", row[1]
   print "ADDRESS = ", row[2]
   print "SALARY = ", row[3], "\n"

print "Operation done successfully";
conn.close()

当上述程序被执行时，将会产生以下结果。

Opened database successfully
Total number of rows deleted : 1
ID = 1
NAME = Paul
ADDRESS = California
SALARY = 20000.0

ID = 3
NAME = Teddy
ADDRESS = Norway
SALARY = 20000.0

ID = 4
NAME = Mark
ADDRESS = Rich-Mond
SALARY = 65000.0

Operation done successfully