Python 操作 PostgreSQL 数据库示例【连接、增删改查等】

本文实例讲述了Python 操作 PostgreSQL 数据库。分享给大家供大家参考，具体如下：

我使用的是 Python 3.7.0

PostgreSQL可以使用psycopg2模块与Python集成。

sycopg2是用于Python编程语言的PostgreSQL数据库适配器。

psycopg2是非常小，快速，稳定的。您不需要单独安装此模块，因为默认情况下它会随着Python 2.5.x版本一起发布。

pip3 install python-psycopg2
pip3 install psycopg2-binary

连接到数据库

以下Python代码显示了如何连接到现有的数据库。如果数据库不存在，那么它将自动创建，最后将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")

在这里指定使用testdb作为数据库名称，如果数据库已成功打开连接，则会提供以下消息：

Open database successfully

创建表

以下Python程序将用于在先前创建的数据库(testdb)中创建一个表：

#!/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()

当执行上述程序时，它将在数据库testdb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述示例中创建的COMPANY表中创建记录：

#!/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("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()

当执行上述程序时，它将在COMPANY表中创建/插入给定的记录，并显示以下两行：

Opened database successfully
Records created successfully

SELECT操作

以下 Python 程序显示了如何从上述示例中创建的 COMPANY 表中获取和显示记录：

#!/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()

执行上述程序时，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

以下 Python 代码显示了如何使用UPDATE语句来更新任何记录，然后从COMPANY表中获取并显示更新的记录：

#!/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

执行上述程序时，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

以下 Python 代码显示了如何使用 DELETE 语句来删除记录，然后从 COMPANY 表中获取并显示剩余的记录：

#!/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("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()

执行上述程序时，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

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希望本文所述对大家Python程序设计有所帮助。

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