Python之sqlite3

Python sqlite3數據庫是一款非常小巧的內置模塊，它使用一個文件存儲整個數據庫，操作十分方便，相比其他大型數據庫來說，確實有些差距。但是在性能表現上並不遜色，麻雀雖小，五臟俱全，sqlite3實現了多少sql-92標准，比如說transaction、trigger和復雜的查詢等。

描述

　　Python的數據庫模塊有統一的接口標准，所以數據庫操作都有統一的模式（假設數據庫模塊名為db）：

　　1. 用db.connect創建數據庫連接，假設連接對象為conn

　　2. 如果該數據庫操作不需要返回結果，就直接使用conn.execute查詢，根據數據庫事物隔離級別的不同，可能修改數據庫需要conn.commit

　　3. 如果需要返回查詢結果則用conn.cursor創建游標對象cur,通過cur.execute查詢數據庫，cursor方法有fetchall、fetchone、fetchmany返回查詢結果，根據數據庫事物隔離級別不同，可能修改數據庫需要coon.commit

　　4. 關閉cur.close

sqlite3基本操作用例

#coding=utf-8

import sqlite3

conn = sqlite3.connect("sqlite.db")  #創建sqlite.db數據庫
print ("open database success")
conn.execute("drop table IF EXISTS student")
query = """create table IF NOT EXISTS student(
    customer VARCHAR(20),
    produce VARCHAR(40),
    amount FLOAT,
    date DATE   
);"""
conn.execute(query)
print ("Table created successfully")

#在表中插入數據

''' 方法1 '''
#data = '''INSERT INTO student(customer,produce,amount,date)\
#    VALUES("zhangsan","notepad",999,"2017-01-02")'''
#conn.execute(data)
#data = '''INSERT INTO student(customer,produce,amount,date)\
#    VALUES("lishi","binder",3.45,"2017-04-05")'''
#conn.execute(data)
#conn.commit()

''' 方法2 '''
statement = "INSERT INTO student VALUES(?,?,?,?)"
data = [("zhangsan","notepad",999,"2017-01-02"),("lishi","binder",3.45,"2017-04-05")]
conn.executemany(statement, data)
conn.commit()

curson = conn.execute("select * from student")
conn.commit()
print (curson)
rows = curson.fetchall()
print (rows)
conn.close()

sqlite3 csv->db->csv

'''將csv數據導入數據庫'''
import sys
import csv
import sqlite3

#解析csv文件
def parsecsvFile(filepath):
    header = None
    data = []
    with open(filepath, 'r') as csvfile:
        filereader = csv.reader(csvfile)
        header = next(filereader)
        #print (header)
        for row in filereader:
            data.append(row)
        #print (data)
    return header,data

#使用sqlite3寫數據庫
def initdb(header, data):
    conn = sqlite3.connect("sqlite.db")
    print ("connect database success")
    conn.execute("drop table IF EXISTS student")
    conn.commit()
    query = '''create table IF NOT EXISTS student(\
        Supplier Name VARCHAR(32),
        Invoice Number VARCHAR(16),
        Part Number VARCHAR(16),
        Cost VARCHAR(16),
        Purchase Date DATE);'''
    conn.execute(query)
    conn.commit() 
    statement = "INSERT INTO student VALUES(?,?,?,?,?)"
    conn.executemany(statement, data)
    conn.commit()
    curson = conn.execute("select * from student")
    conn.commit()
    print (curson)
    rows = curson.fetchall()
    print (rows)
    conn.close()
    return rows

#根據數據庫內容寫csv文件
def wirtecsvfile(writefilepath, header, data):
    with open(writefilepath, 'a+') as writefile:
        writer = csv.writer(writefile, delimiter=",")
        writer.writerow(header)
        for row in data:
            writer.writerow(row)
    
if __name__ == "__main__":
    readfilepath = sys.argv[1]
    writefilepath = sys.argv[2]
    header,data = parsecsvFile(readfilepath)
    rows = initdb(header, data)
    wirtecsvfile(writefilepath, header, rows)