Python连接PostgreSQL数据库
目录
Python连接PostgreSQL数据库
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。 如果还没有在您的机器上安装它，那么可以使用yum命令安装它，如下所示：
$yum install python-psycopg2
要使用psycopg2模块，必须首先创建一个表示数据库的Connection对象，然后可以选择创建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()
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
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