将Python 连接到PostgreSQL 数据库实例代码方法

terry 2年前 (2023-09-26) 阅读数 45 #数据库

PostgreSQL 可以使用psycopg2 模块与Python 集成。 sycopg2 是适用于 Python 编程语言的 PostgreSQL 数据库适配器。 psycopg2非常小、快速且稳定。您不需要单独安装此模块，因为它默认随 Python 2.5.x 一起提供。如果您的计算机上尚未安装，您可以使用 yum 命令进行安装，如下所示：

$yum install python-psycopg2

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要使用 psycopg2 模块，您必须首先创建代表数据库的连接对象，然后可以选择创建一个可以帮助您执行所有SQL语句的游标对象。

`连接到数据库`

以下 Python 代码显示如何连接到现有数据库。如果数据库不存在，则自动创建，最后返回一个数据库对象。

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")

print "Opened database successfully"

Python 进入此处使用testdb作为数据库名称，如果数据库成功打开连接，则会显示以下消息：♷Shell‸♸″reShell⿓ 要创建表，将在之前创建的数据库 (testdb) 中使用以下 Python 程序： 
#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print "Opened database successfully"

cur = conn.cursor()
cur.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.commit()
conn.close()
Python 运行上述程序后， testdb

COMPANY 将在数据库中创建并显示以下消息：

Opened database successfully
Table created successfully

Shell

插入操作

以下 Python 程序显示如何在上例中创建的 COM PA 中创建条目：

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print "Opened database successfully"

cur = conn.cursor()

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

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

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

cur.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()

Python

当上面的程序运行时，它会创建/插入给定的记录到表 COMPANY 并显示以下两行：

Opened database successfully
Records created successfully

SELECT 操作

下面是一个 Python 程序，显示如何从上例中创建的表 COMPANY 中检索和显示记录：

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print "Opened database successfully"

cur = conn.cursor()

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

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

，Python 程序

将在创建时运行：

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

Shell

更新操作

以下 Python 代码显示如何使用命令 UPDATE 更新任何记录及其随后从 的加载获取并显示 COMPANY 表中更新的记录：

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print "Opened database successfully"

cur = conn.cursor()

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

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

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

Python

运行上述程序会产生以下结果：

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

Shell

♝删除以下代码使用命令 DELETE 删除记录，然后获取并显示表中剩余的记录 COMPANY：

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database="testdb", user="postgres", password="pass123", host="127.0.0.1", port="5432")
print "Opened database successfully"

cur = conn.cursor()

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

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

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

Python

运行时产生上述结果：

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

Shell