python 操做PostgreSQL

pip install psycopg

Python psycopg2 模塊APIs

如下是psycopg2的重要的的模塊例程能夠知足Python程序與PostgreSQL數據庫的工做。

 

 

 

S.N.	API & 描述
1	psycopg2.connect(database="testdb", user="postgres", password="cohondob", host="127.0.0.1", port="5432")  這個API打開一個鏈接到PostgreSQL數據庫。若是成功打開數據庫時，它返回一個鏈接對象。 www.yiibai.com
2	connection.cursor() 該程序建立一個光標將用於整個數據庫使用Python編程。 yiibai.com
3	cursor.execute(sql [, optional parameters]) 此例程執行SQL語句。可被參數化的SQL語句（即佔位符，而不是SQL文字）。 psycopg2的模塊支持佔位符用％s標誌 yiibai.com 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命令對全部參數序列或序列中的sql映射。 www.yiibai.com
5	curosr.callproc(procname[, parameters]) 這個程序執行的存儲數據庫程序給定的名稱。該程序預計爲每個參數，參數的順序必須包含一個條目。
6	cursor.rowcount 這個只讀屬性，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。若是不調用這個方法，不管作了什麼修改，自從上次調用commit()是不可見的，從其餘的數據庫鏈接。
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() 此方法關閉數據庫鏈接。請注意，這並不自動調用commit（）。若是你只是關閉數據庫鏈接而不調用commit（）方法首先，那麼全部更改將會丟失！ www.yiibai.com
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，或者無當沒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。當沒有找到記錄，返回空列表。該方法試圖獲取儘量多的行所顯示的大小參數。
12	cursor.fetchall() 這個例程獲取全部查詢結果（剩餘）行，返回一個列表。空行時則返回空列表。 www.yiibai.com

鏈接到數據庫

Python代碼顯示瞭如何鏈接到一個現有的數據庫。若是數據庫不存在，那麼它就會被建立，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" 

建立表

如下Python程序將使用之前建立的數據庫中建立一個表：

#!/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()

INSERT 操做

Python程序顯示了咱們如何建立表COMPANY 在上面的例子中建立表中的記錄：

#!/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()

SELECT 操做

Python程序，顯示如何獲取並顯示COMPANY 表在上面的例子中建立的記錄：

#!/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], "\n"

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

當上述程序執行時，它會產生如下結果

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 操做

Python代碼顯示如何，咱們能夠使用UPDATE語句來更新記錄，而後從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], "\n"

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

DELETE 操做

Python代碼顯示瞭如何咱們能夠使用DELETE語句刪除記錄，而後獲取並顯示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], "\n"

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