python 操作PostgreSQL
pip install psycopg
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。
| S.N. | API & 描述 |
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| 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。 www.yiibai.com |
| 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。 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（即占位符，而不是SQL文字）。 psycopg2的模塊支持占位符用％s標誌 yiibai.com 例如：cursor.execute("insert into people values (%s, %s)", (who, age))
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| 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。 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。該程序預計為每一個參數，參數的順序必須包含一個條目。
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| 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*().
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| 7 | connection.commit() 此方法提交當前事務。如果不調用這個方法，無論做了什麽修改，自從上次調用commit()是不可見的，從其他的數據庫連接。
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| 8 | connection.rollback() 此方法會回滾任何更改數據庫自上次調用commit（）方法。
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| 9 | connection.close() 此方法關閉數據庫連接。請註意，這並不自動調用commit（）。如果你只是關閉數據庫連接而不調用commit（）方法首先，那麽所有更改將會丟失！ 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。
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| 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。該方法試圖獲取盡可能多的行所顯示的大小參數。
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| 12 | cursor.fetchall() 這個例程獲取所有查詢結果（剩余）行，返回一個列表。空行時則返回空列表。 www.yiibai.com
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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，那麽它就會被創建，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"
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()
INSERT 操作
Python程序顯示了我們如何創建表COMPANY 在上面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()
SELECT 操作
Python程序，顯示如何獲取並顯示COMPANY 表在上面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], "\n" 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], "\n" print "Operation done successfully"; conn.close()
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 表剩余的記錄：
#!/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()
python 操作PostgreSQL