Python之sqlite3

Posted 2020-10-25 Fate0729

Python sqlite3数据库是一款非常小巧的内置模块，它使用一个文件存储整个数据库，操作十分方便，相比其他大型数据库来说，确实有些差距。但是在性能表现上并不逊色，麻雀虽小，五脏俱全，sqlite3实现了多少sql-92标准，比如说transaction、trigger和复杂的查询等。

描述

　　Python的数据库模块有统一的接口标准，所以数据库操作都有统一的模式（假设数据库模块名为db）：

　　1. 用db.connect创建数据库连接，假设连接对象为conn

　　2. 如果该数据库操作不需要返回结果，就直接使用conn.execute查询，根据数据库事物隔离级别的不同，可能修改数据库需要conn.commit

　　3. 如果需要返回查询结果则用conn.cursor创建游标对象cur,通过cur.execute查询数据库，cursor方法有fetchall、fetchone、fetchmany返回查询结果，根据数据库事物隔离级别不同，可能修改数据库需要coon.commit

　　4. 关闭cur.close

sqlite3基本操作用例

#coding=utf-8

import sqlite3

conn = sqlite3.connect("sqlite.db")  #创建sqlite.db数据库
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")

#在表中插入数据

‘‘‘ 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

‘‘‘将csv数据导入数据库‘‘‘
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写数据库
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

#根据数据库内容写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)