PostgreSQL Python 接口

安装

PostgreSQL 可以使用 psycopg2 模块与 Python 集成。sycopg2 是 Python 编程语言的 PostgreSQL 数据库适配器。编写 psycopg2 的目的是使其轻便和快速，并且稳定。我们不需要单独安装此模块，因为默认情况下它随 Python 2.5.x 版一起提供。

如果你的机器上没有安装它，那么你可以使用 yum 命令来安装它，如下所示 -

$yum install python-psycopg2

要使用 psycopg2 模块，必须首先创建一个代表数据库的 Connection 对象，然后选择创建游标对象，这将对你执行所有 SQL 语句有很大的帮助。

连接到数据库

以下 Python 代码显示了如何连接到现有数据库。如果数据库不存在，则将创建它并最终返回一个数据库对象。

#!/usr/bin/python

import psycopg2

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

print "Opened database successfully"

在这里，您还可以提供数据库 jiyik_db 作为名称，如果数据库成功连接，则会显示以下消息

Open database successfully

创建表

以下 Python 程序将用于在先前创建的数据库中创建表

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database = "jiyik_db", 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()

当上面给定的程序被执行时，它会在你的 jiyik_db 中创建 COMPANY 表，并且显示以下消息

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 psycopg2

conn = psycopg2.connect(database = "jiyik_db", 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()

当执行上述给定的程序时，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

选择操作

以下 Python 程序显示了我们如何从上面示例中创建的 COMPANY 表中获取数据，并且显示记录

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database = "jiyik_db", 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()

当上面给定的程序被执行时，它会产生以下结果

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 代码展示了我们如何使用 UPDATE 语句来更新任何记录，然后从我们的 COMPANY 表中获取更新后的数据，并显示出来

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database = "jiyik_db", 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()

当上面给定的程序被执行时，它会产生以下结果

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

删除操作

下面的 Python 代码展示了我们如何使用 DELETE 语句删除记录，然后从我们的 COMPANY 表中获取并显示剩余的记录

#!/usr/bin/python

import psycopg2

conn = psycopg2.connect(database = "jiyik_db", 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()

当上面给定的程序被执行时，它会产生以下结果 -

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