Postgresql 简明教程
PostgreSQL - Python Interface
Installation
可以使用 psycopg2 模块与 Python 集成 PostgreSQL。psycopg2 是用于 Python 编程语言的 PostgreSQL 数据库适配器。编写 psycopg2 的目的是使其体积非常小、速度非常快、稳定性非常高。您无需单独安装此模块,因为在默认情况下它已随 Python 版本 2.5.x 及更高版本一同发货。
如果您在自己的电脑上未安装它,那么您可以使用 yum 命令如下安装它 −
$yum install python-psycopg2
要使用 psycopg2 模块,您必须先创建一个表示数据库的连接对象,然后还可以选择创建一个游标对象,它将帮助您执行所有 SQL 语句。
Python psycopg2 module APIs
以下是重要的 psycopg2 模块例程,它足以满足您通过 Python 程序使用 PostgreSQL 数据库的需求。如果您正在寻找更复杂的应用程序,那么您可以查阅 Python psycopg2 模块的官方文档。
S. No. |
API & Description |
1 |
psycopg2.connect(database="testdb", user="postgres", password="cohondob", host="127.0.0.1", port="5432") 此 API 打开与 PostgreSQL 数据库的连接。如果数据库打开成功,它将返回一个连接对象。 |
2 |
connection.cursor() 此例程创建将用 Python 的数据库编程中使用的 cursor 。 |
3 |
cursor.execute(sql [, optional parameters]) 此例程执行 SQL 语句。SQL 语句可以参数化(即占位符代替 SQL 文字)。 psycopg2 模块使用 %s 符号支持占位符,例如: cursor.execute("insert into people values (%s, %s)", (who, age)) |
4 |
cursor.executemany(sql, seq_of_parameters) 此例程针对序列 sql 中找到的所有参数序列或映射执行 SQL 命令。 |
5 |
cursor.callproc(procname[, parameters]) 此例程使用给定的名称执行存储的数据库过程。参数序列必须包含过程所需每个参数的一个条目。 |
6 |
cursor.rowcount 此只读属性返回最后一次 execute*() 修改、插入或删除的数据库总行数。 |
7 |
connection.commit() 此方法提交当前事务。如果你不调用此方法,那么自上次调用 commit() 之后所做的一切对其他数据库连接不可见。 |
8 |
connection.rollback() 此方法回滚自上次调用 commit() 以来对数据库的任何更改。 |
9 |
connection.close() 此方法关闭数据库连接。请注意,这不自动调用 commit()。如果您在不先调用 commit() 的情况下关闭数据库连接,您的更改将会丢失! |
10 |
cursor.fetchone() 此方法获取查询结果集的下一行,返回一个序列,或者在没有更多数据可用时返回 None。 |
11 |
cursor.fetchmany([size=cursor.arraysize]) 此例程获取结果集合中的下一组行,返回一个列表。如果没有更多行可用,则返回一个空列表。该方法会尝试获取 size 参数指示的行数。 |
12 |
cursor.fetchall() 该例程获取查询结果的所有(剩余)行,并返回一个列表。当没有可用行时返回一个空列表。 |
Connecting to Database
下面的 Python 代码展示如何连接到一个现有数据库。如果数据库不存在,则会创建数据库并最终返回数据库对象。
#!/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"
在此,你也可以提供数据库 testdb 作为名称,并且如果数据库成功打开,则会给出以下消息:
Open database successfully
Create a Table
下面的 Python 程序用于在之前创建的数据库中创建一个表:
#!/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()
当执行上述给定程序时,它会在你的 test.db 中创建 COMPANY 表,并且它会显示以下消息:
Opened database successfully
Table created successfully
INSERT Operation
下面的 Python 程序展示了我们如何能够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()
当执行给定上面的程序时,它将在 COMPANY 表中创建给定的记录,然后显示以下两行 −
Opened database successfully
Records created successfully
SELECT Operation
下面的 Python 程序展示了我们如何能够从上面示例中创建的 COMPANY 表中获取和展示记录:
#!/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()
当执行给定上面的程序时,它将产生以下结果 −
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
UPDATE Operation
下面的 Python 代码展示了我们如何能够使用 UPDATE 语句来更新任何记录,然后从 COMPANY 表中获取和展示更新的记录:
#!/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()
当执行给定上面的程序时,它将产生以下结果 −
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
DELETE Operation
下面的 Python 代码展示了我们如何能够使用 DELETE 语句来删除任何记录,然后从 COMPANY 表中获取和展示剩余的记录:
#!/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()
当执行给定上面的程序时,它将产生以下结果 −
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