让Python帮你搞定MySQL数据库

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mysql是常用的数据库之一，也是面试工作必备技能之一。

本文通过一个实战，将Python与SQL语句结合起来使用，搞定MySQL数据库。

// 实战开始 //

我们在github上下载fifa18球员数据，将这些信息存入到mysql。
①数据下载地址：
https://github.com/amanthedorkknight/fifa18-all-player-statistics
②选择：Complete->basicplayerdata.csv

// 将数据从CSV导入到MySQL //

1）创建对应库与表 

#创建公司数据库，编码格式utf-8CREATE DATABASE fifa18_db DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;#选择数据库：use fifa18_db;#创建球员表：id,名称，海报地址，俱乐部，年龄，薪资等，与csv文件对应create table player(id int Primary key auto_increment, player_id int, name char(64), age int, poster char(64),
 flag char(64), overall int, potential int, club char(64) default '', club_Logo char(64),  value char(16), wage char(16), special int) default charset =utf8;

2）CSV读取文件

数据集中某些球员字段为空，插入时候需要补充默认值，使用DictReader读取。 

path = '/home/linux/workdir/data/basicplayerdata.csv'#字段名称field = ['','ID','Name','Age','Photo','Nationality','Flag','Overall','Potential','Club','Club Logo','Value','Wage','Special']f = open(path)fcsv = csv.DictReader(f, fieldnames = field)#第一行去掉line = next(fcsv)#第一行有效数据line = next(fcsv)print(line)

结果： 

OrderedDict([('', '0'), ('ID', '158023'), ('Name', 'L. Messi'), ('Age', '30'), ('Photo', 'https://cdn.sofifa.org/players/4/18/158023.png'), ('Nationality', 'Argentina'), ('Flag', 'https://cdn.sofifa.org/flags/52.png'), ('Overall', '94'), ('Potential', '94'), ('Club', 'FC Barcelona'), ('Club Logo', 'https://cdn.sofifa.org/teams/2/18/light/241.png'), ('Value', '€118.5M'), ('Wage', '€565K'), ('Special', '2161')])

3）读取一行并整理数据格式

CSV读取字段与数据库对应起来，且不要CSV文件种的第一列，整理数据格式为字典，key为数据库列名，value为CSV对应内容，代码实现。 

sqlfield = ['player_id','name','age','poster','nationality','flag','overall','potential','club','club_logo','value','wage','special']csvfield = ['ID','Name','Age','Photo','Nationality','Flag','Overall','Potential','Club','Club Logo','Value','Wage','Special']#转成字典：keysinfo = dict(zip(sqlfield, csvfield))#填充数据：data = {}for sfield, cfield in keysinfo.items(): ele = line.get(cfield, '') data.setdefault(sfield, ele)print(data)

结果： 

{'player_id': '158023', 'name': 'L. Messi', 'age': '30', 'poster': 'https://cdn.sofifa.org/players/4/18/158023.png', 'nationality': 'Argentina', 'flag': 'https://cdn.sofifa.org/flags/52.png', 'overall': '94', 'potential': '94', 'club': 'FC Barcelona', 'club_logo': 'https://cdn.sofifa.org/teams/2/18/light/241.png', 'value': '€118.5M', 'wage': '€565K', 'special': '2161'}

4）拼接sql语句

尝试插入一条数据：获取插入字段与对应数据，拼接成sql语句。 

tablename = 'player'keys = data.keys()fields = ','.join(keys)vals = ','.join(["'%s'"% val for val in data.values()])sql = f"INSERT INTO {tablename}({fields}) VALUES({vals})"print(sql)

结果： 

INSERT INTO player(player_id,name,age,poster,nationality,flag,overall,potential,club,club_logo,value,wage,special) VALUES('158023','L. Messi','30','https://cdn.sofifa.org/players/4/18/158023.png','Argentina','https://cdn.sofifa.org/flags/52.png','94','94','FC Barcelona','https://cdn.sofifa.org/teams/2/18/light/241.png','€118.5M','€565K','2161')

5）连接数据库，并插入数据 

#编码格式：utf-8db = pymysql.connect("localhost","root","abc123","fifa18_db", charset='utf8')#获取游标cursor = db.cursor()cursor.execute(sql)#提交数据db.commit()#断开连接cursor.close()db.close()

查看player中信息，插入成功。


基本功能都已经实现，对代码进行整理，根据功能定义类及方法。 

import csvimport pymysqlclass LoadDataFromCsvToMysql: def __init__(self, csvpath, csvfield, mysqlfield, table, sqlconfig): #初始化参数 pass def connectSql(self): #连接数据库，获取游标 pass def disconnectSql(self): #断开数据库，获取游标 pass def processSql(self, sql): #处理sql语句 pass def loadCsv(self): #打开csv文件，返回csv对象 pass def closeCsv(self): #关闭csv文件 pass def gensql(self, linedata): #生成sql语句 pass def process(self): #对外接口，打开文件并写数据库 pass

类定义完成之后，我们可以将功能明确的方法实现。 

import csvimport pymysqlclass LoadDataFromCsvToMysql: def __init__(self, csvpath, csvfield, mysqlfield, table, sqlconfig): #初始化参数 self.dbconfig = sqlconfig self.inpath = csvpath self.sqlfield = mysqlfield self.csvfield = csvfield self.fieldmap = dict(zip(mysqlfield, csvfield[1:])) self.tablename = table def connectSql(self): self.db = pymysql.connect(**self.dbconfig, charset='utf8') self.cursor = self.db.cursor() def disconnectSql(self): self.cursor.close() self.db.close() def processSql(self, sql): ret = self.cursor.execute(sql) self.db.commit() return ret def loadCsv(self): #打开csv文件 self.f = open(path) fcsv = csv.DictReader(self.f, fieldnames = self.csvfield) next(fcsv) return fcsv def closeCsv(self): self.f.close() def gensql(self, linedata): pass def process(self): #测试数据库与csv文件打开关闭 self.connectSql() print('connect sql...') fcsv = self.loadCsv() self.disconnectSql() self.closeCsv() print('disconnect sql') path = '/home/linux/workdir/data/basicplayerdata.csv'sqlfield= ['player_id','name','age','poster','nationality','flag','overall','potential','club','club_logo','value','wage','special']csvfield = ['','ID','Name','Age','Photo','Nationality','Flag','Overall','Potential','Club','Club Logo','Value','Wage','Special']dbconfig = {'host':'localhost','port':3306,'user':'root','passwd':'abc123','db':'fifa18_db'}obj = LoadDataFromCsvToMysql(path, csvfield, sqlfield, 'player', dbconfig)obj.process()

输出： 

connect sql...load csvfiledisconnect sql

6）完善process与gensql

先完善process方法实现： 

 def process(self): #测试数据库与csv文件打开关闭 self.connectSql() print('connect sql...') fcsv = self.loadCsv() for line in fcsv: sql = self.gensql(line) print(sql) n = self.processSql(sql) self.disconnectSql() self.closeCsv() print('disconnect sql')

然后完善gensql方法，将前面实现添加到此方法中。 

def gensql(self, linedata): #产生sql语句 data = {} for sfield, cfield in self.fieldmap.items(): ele = linedata.get(cfield, '') data.setdefault(sfield, ele) tablename = self.tablename keys = data.keys() fields = ','.join(keys) vals = ','.join(["'%s'"% val for val in data.values()]) sql = f"INSERT INTO {tablename}({fields}) VALUES({vals})" return sql

测试前将player表中内容删除，然后使用代码先插入一条，并查看结果；如果测试没有问题，可以插入所有数据。实际运行出现问题：sql语句错误 ，字符串拼接错误。

出错sql语句： 

"('158023','L. Messi','30','https://cdn.sofifa.org/players/4/18/158023.png',..)"

双引号+单引号，但是文件中，某些字符串带单引号，所以出现字段错误。

修改sql拼接方法： 

 def gensql(self, linedata): #产生sql语句 data = {} for sfield, cfield in self.fieldmap.items(): ele = linedata.get(cfield, '') data.setdefault(sfield, ele) tablename = self.tablename keys = data.keys() fields = ','.join(keys) vals = ','.join(['"%s"'% val for val in data.values()]) sql = f'INSERT INTO {tablename}({fields}) VALUES({vals})' return sql

运行结果： 

dstram","18","https://cdn.sofifa.org/players/4/18/238813.png","England","https://cdn.sofifa.org/flags/14.png","47","65","Crewe Alexandra","https://cdn.sofifa.org/teams/2/18/light/121.png","€60K","€1K","1305")INSERT INTO player(player_id,name,age,poster,nationality,flag,overall,potential,club,club_logo,value,wage,special) VALUES("238306","A. Conway","19","https://cdn.sofifa.org/players/4/18/238306.png","Republic of Ireland","https://cdn.sofifa.org/flags/25.png","47","63","Galway United","https://cdn.sofifa.org/teams/2/18/light/1571.png","€60K","€1K","1314")disconnect sql1555235373.5942054 1555235392.2122808

插入18000条数据，花费时间大概为20S左右；后续优化：每次插入500条数据，然后在查看花费时间，这个大家可以参考前面案例自己实现。

// 在SQL中查询数据 //

需求：查询player表中阿根廷国家球员姓名，年龄，头像信息。读者朋友可以自己尝试去实现，考虑使用继承。

①sql中查询数据我们步骤：连接数据库，执行sql语句，关闭数据库；
②查询与写入很多方法通用，考虑继承LoadDataFromCsvToMysql类；
③需要重载init，process，processSql方法；

代码实现： 

class QueryMysql(LoadDataFromCsvToMysql): def __init__(self, sqlconfig): #调用父类方法，初始化传一些无效参数 super(QueryMysql, self).__init__('',[], [], '', dbconfig) def genSql(self, table, fields, condition=None): #查询语句生成 fds = ','.join(fields) cond = '' print(condition) if condition: cond = f' where {condition}' sql = f'select {fds} from {table}{cond}' return sql def process(self, tablename, fields, condition=None): #对外接口 #调用父类中的连接数据库，关闭数据库方法 self.connectSql() sql = self.genSql(tablename, fields, condition) self.processSql(sql) items = self.cursor.fetchall() for item in items: print(item) print('all Argentina player:', len(items)) self.disconnectSql() dbconfig= {'host':'localhost','port':3306,'user':'root','passwd':'abc123','db':'fifa18_db'}tablename = 'player'files = ['name','poster', 'age']obj = QueryMysql(dbconfig)cond = 'nationality="Argentina"'obj.process(tablename, files, cond)

结果： 

('L. Messi', 'https://cdn.sofifa.org/players/4/18/158023.png', 30)('G. Higuaín', 'https://cdn.sofifa.org/players/4/18/167664.png', 29)('P. Dybala', 'https://cdn.sofifa.org/players/4/18/211110.png', 23)...('A. Miño', 'https://cdn.sofifa.org/players/4/18/243298.png', 23)('T. Durso', 'https://cdn.sofifa.org/players/4/18/240955.png', 18)('K. Humeler', 'https://cdn.sofifa.org/players/4/18/240291.png', 20)('J. Mendive', 'https://cdn.sofifa.org/players/4/18/241584.png', 20)all Argentina player: 966

结果：

数据集中一共有966名Argentina球员。



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