如何将 postgresql 连接到 python

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。 psycopg2 非常小、快速且稳定。你不需要单独安装此模块，因为它默认随 Python 2.5.x 版本一起提供。如果你的机器上尚未安装它，则可以使用 yum 命令安装它，如下所示：

$yum install python-psycopg2

要使用 psycopg2 模块，你必须首先创建一个代表数据库的 Connection 对象，然后可选择创建一个游标对象来帮助你执行所有 SQL 语句。

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，会自动创建，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"

此处指定使用 testdb 作为数据库名称，如果数据库已成功打开连接，将给出以下消息：

Open database successfully

创建表

下面的 Python 程序将用于在之前创建的数据库（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()

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面示例中创建的 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()

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

Opened database successfully
Records created successfully

SELECT操作

以下 Python 程序展示了如何从上例中创建的 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 语句更新任何记录，然后从 COMPANY 表中获取并显示更新后的记录：

#!/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()

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 语句删除记录，然后从 COMPANY 表中获取并显示剩余记录：

#!/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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