PostgreSQL Python 接口
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 的目的是非常小和快速,并且像岩石一样稳定。你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,你必须首先创建一个代表数据库的 Connection 对象,然后你可以选择创建游标对象,这将帮助你执行所有 SQL 语句。
Python psycopg2 模块 API
以下是重要的 psycopg2 模块例程,它们可以满足你从 Python 程序使用 PostgreSQL 数据库的要求。如果你正在寻找更复杂的应用程序,那么你可以查看 Python psycopg2 模块的官方文档。
序号 | API & 描述 |
---|---|
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,它返回一个连接对象。 |
2 |
connection.cursor() 此例程创建一个 cursor 它将在你使用 Python 进行数据库编程的整个过程中使用。 |
3 |
cursor.execute(sql [, 可选参数]) 该例程执行 SQL 语句。 SQL 语句可以参数化(即,占位符而不是 SQL 文字)。 psycopg2 模块支持使用 %s 符号的占位符 例如:cursor.execute("insert into people values (%s, %s)", (who, age)) |
4 |
cursor.executemany(sql,seq_of_parameters) 此例程针对在序列 sql 中找到的所有参数序列或映射执行 SQL 命令。 |
5 |
cursor.callproc(procname[, 参数]) 此例程执行具有给定名称的存储数据库过程。对于过程期望的每个参数,参数序列必须包含一个条目。 |
6 |
游标.rowcount 此只读属性返回由上次执行*() 修改、插入或删除的数据库行总数。 |
7 |
连接提交() 此方法提交当前事务。如果不调用此方法,则自上次调用 commit() 以来所做的任何事情都不会从其他数据库连接中看到。 |
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 |
连接.close() 此方法关闭数据库连接。请注意,这不会自动调用 commit()。如果你在没有先调用 commit() 的情况下关闭数据库连接,你的更改将会丢失! |
10 |
cursor.fetchone() 此方法获取查询结果集的下一行,返回单个序列,或者在没有更多数据可用时返回 None。 |
11 |
cursor.fetchmany([size=cursor.arraysize]) 该例程获取查询结果的下一组行,返回一个列表。当没有更多行可用时,将返回一个空列表。该方法尝试获取由 size 参数指示的尽可能多的行。 |
12 |
cursor.fetchall() 此例程获取查询结果的所有(剩余)行,返回一个列表。当没有可用行时,返回一个空列表。 |
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="testdb", user = "postgres", password = "pass123", host = "127.0.0.1", port = "5432") print "Opened database successfully"
在这里,你还可以提供数据库 testdb 作为名称,如果数据库成功打开,则会给出以下信息:
Open database successfully
创建表
以下 Python 程序将用于在之前创建的数据库中创建表:
#!/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()
当上面给出的程序被执行时,它会在你的目录中创建 COMPANY 表 test.db 它将显示以下消息:
Opened database successfully Table created successfully
插入操作
以下 Python 程序展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()
当上面给定的程序被执行时,它会在 COMPANY 表中创建给定的记录,并会显示以下两行:
Opened database successfully Records created successfully
选择操作
下面的 Python 程序展示了我们如何从上面示例中创建的 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()
当上面给出的程序被执行时,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
以下 Python 代码展示了如何使用 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()
当上面给出的程序被执行时,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
以下 Python 代码展示了如何使用 DELETE 语句删除任何记录,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()
当上面给出的程序被执行时,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