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PostgreSQL連接Python

安裝

PostgreSQL可以用Python psycopg2模塊集成。 sycopg2是Python編程語言的PostgreSQL數據庫的適配器。 其程序代碼少,速度快,穩定。不需要單獨安裝這個模塊,因為它默認情況下被運往隨著Python版本在2.5.x一起的。如果不把它安裝在機器上,然後可以使用yum命令安裝它,如下所示:

$yum install python-psycopg2

要使用psycopg2的模塊,首先必須創建一個Connection對象,它表示數據庫然後再可以選擇創建遊標對象,這將幫助執行的所有SQL語句。

Python psycopg2 模塊APIs

以下是psycopg2的重要的的模塊例程可以滿足Python程序與PostgreSQL數據庫的工作。如果尋找一個更複雜的應用程序,那麼可以看看Python psycopg2的模塊的官方文檔。

S.N. API & 描述
1 psycopg2.connect(database="testdb", user="postgres", password="cohondob", host="127.0.0.1", port="5432")

這個API打開一個連接到PostgreSQL數據庫。如果成功打開數據庫時,它返回一個連接對象。

2 connection.cursor()

該程序創建一個光標將用於整個數據庫使用Python編程。

3 cursor.execute(sql [, optional parameters])

此例程執行SQL語句。可被參數化的SQL語句(即占位符,而不是SQL文字)。 psycopg2的模塊支持占位符用%s標誌

例如:cursor.execute("insert into people values (%s, %s)", (who, age))

4 curosr.executemany(sql, seq_of_parameters)

該程序執行SQL命令對所有參數序列或序列中的sql映射。

5 curosr.callproc(procname[, parameters])

這個程序執行的存儲數據庫程序給定的名稱。該程序預計為每一個參數,參數的順序必須包含一個條目。

6 cursor.rowcount

這個隻讀屬性,它返回數據庫中的行的總數已修改,插入或刪除最後 execute*().

7 connection.commit()

此方法提交當前事務。如果不調用這個方法,無論做了什麼修改,自從上次調用commit()是不可見的,從其他的數據庫連接。

8 connection.rollback()

此方法會回滾任何更改數據庫自上次調用commit()方法。

9 connection.close()

此方法關閉數據庫連接。請注意,這並不自動調用commit()。如果你隻是關閉數據庫連接而不調用commit()方法首先,那麼所有更改將會丟失!

10 cursor.fetchone()

這種方法提取的查詢結果集的下一行,返回一個序列,或者無當冇有更多的數據是可用的。

11 cursor.fetchmany([size=cursor.arraysize])

這個例程中取出下一個組的查詢結果的行數,返回一個列表。當冇有找到記錄,返回空列表。該方法試圖獲取儘可能多的行所顯示的大小參數。

12 cursor.fetchall()

這個例程獲取所有查詢結果(剩餘)行,返回一個列表。空行時則返回空列表。

連接到數據庫

Python代碼顯示了如何連接到一個現有的數據庫。如果數據庫不存在,那麼它就會被創建,最終將返回一個數據庫對象。

#!/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"

在這裡,也可以提供數據庫testdb的名稱,如果數據庫成功打開,那麼它會給下麵的消息:

Open database successfully

創建表

以下Python程序將使用以前創建的數據庫中創建一個表:

#!/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()

上述程序執行時,它會創建表COMPANY 在數據庫test.db中,它會顯示以下消息:

Opened database successfully
Table created successfully

INSERT 操作

Python程序顯示了我們如何創建表COMPANY 在上麵的例子中創建表中的記錄:

#!/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()

上述程序執行時,它會創建COMPANY表中的記錄,並顯示以下兩行:

Opened database successfully
Records created successfully

SELECT 操作

Python程序,顯示如何獲取並顯示COMPANY 表在上麵的例子中創建的記錄:

#!/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], "
"

print "Operation done successfully";
conn.close()

當上述程序執行時,它會產生以下結果:

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 操作

Python代碼顯示如何,我們可以使用UPDATE語句來更新記錄,然後從COMPANY表獲取並顯示更新的記錄:

#!/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], "
"

print "Operation done successfully";
conn.close()

當上述程序執行時,它會產生以下結果:

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 操作

Python代碼顯示了如何我們可以使用DELETE語句刪除記錄,然後獲取並顯示COMPANY 表剩餘的記錄: 

#!/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], "
"

print "Operation done successfully";
conn.close()

當上述程序執行時,它會產生以下結果:

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