What is the author's main argument about the modern city? In the organization of industrial life the influence fo the factory upon the physiological and mental state of the workers has been completely neglected. Mordern industry is based on the conce…
lesson 16 Mary had a little lamb a little + 可数 小的;+ 不可数 少量的 对于动物在幼时都有不同的称呼: calf 小牛 lamb 羊羔 piglet 小猪 kitty 小猫 puppy 小狗 foal 马仔 chick 小鸡 duckling 小鸭子 tiny: very small possess 相比have own比较正式 possession(s) 财产 personal possessions treasured/prized/preci…
Text If you park your car in the wrong place, a traffic policeman will soon find it. You will be very lucky if he lets you go without a ticket. However this does not always happen. Traffic police are sometimes very polite. During a holiday in Sweden,…
这个课程的参考视频和图片来自youtube. 主要学到的知识点有: We want to handle the bad Error. (e.g bad input / bugs in program) Error: a type of Exception e.g File I/O; User Input, out of control. An example that handle the wrong input and out of range input. 1. First we…
全文转载自 Scott Hanselman的博文. I bought a 3D printer on Friday, specifically a Printrbot Simple Metal from Amazon for US$599. I did a few days of research, looking at all the consumer models under $1000. Some were enclosed, others not. Some made of wood,…
#瓦登尔湖词频统计: import string path = 'D:/python3/Walden.txt' with open(path,'r',encoding= 'utf-8') as text: words = [raw_word.strip(string.punctuation).lower() for raw_word in text.read().split()] words_index = set(words) counts_dict = {index:words.count(…
Beginning Game Programming v2.0 Last Updated 8/19/18 Greetings everyone, welcome to the ground up recoding of Beginning Game Programming with SDL. This time we will be coding with SDL 2 which has been released on the SDL website. These tutorials were…
2017/11/24 Regardless of the enormous amount of photos shared on Wechat or Face book, modern city dwellers grow detached from their immediate surroundings and fail to realize that codes and digits can never provide the human touch that we yearn for.…
索引是快速搜索的关键.MySQL索引的建立对于MySQL的高效运行是很重要的.下面介绍几种常见的MySQL索引类型 在数据库表中,对字段建立索引可以大大提高查询速度.假如我们创建了一个 mytable表: CREATE TABLE mytable( ID INT NOT NULL, username VARCHAR(16) NOT NULL );我们随机向里面插入了10000条记录,其中有一条:5555, admin.在查找username="admin"的记录 SELECT * FR…
一.普通索引 这是最基本的索引,它没有任何限制.它有以下几种创建方式: 1.创建索引 CREATE INDEX [indexName] ON [mytable] ([column][(length)],...); 如果是CHAR,VARCHAR类型,length可以小于字段实际长度:如果是BLOB和TEXT类型,必须指定 length. 2.修改表结构 ALTER [mytable] ADD INDEX [indexName] ON ([column][(length)],...) 创建表的时候…
create database ProCityData use Procitydata --创建Province(省表) create table Province ( ProID int primary key, ProName nvarchar(32) not null ) --中国34个省级行政单位 23个省 5个自治区 4个直辖市 2特别行政区 insert into Province values(1,'北京市') insert into Province values(2,'天津市'…
索引是快速搜索的关键.MySQL索引的建立对于MySQL的高效运行是很重要的.下面介绍几种常见的MySQL索引类型. 在数据库表中,对字段建立索引可以大大提高查询速度.假如我们创建了一个 mytable表: CREATE TABLE mytable( ID INT NOT NULL, username VARCHAR(16) NOT NULL ); 我们随机向里面插入了10000条记录,其中有一条:5555, admin. 在查找username="admin"的记录…
Stat2.2x Probability(概率)课程由加州大学伯克利分校(University of California, Berkeley)于2014年在edX平台讲授. PDF笔记下载(Academia.edu) Summary Zeros and Ones: Sum of a sample with replacement $S$ is the number of successes: $n$ independent trials, chance of success on a sing…
索引是快速搜索的关键.MySQL索引的建立对于MySQL的高效运行是很重要的.下面介绍几种常见的MySQL索引类型. 在数据库表中,对字段建立索引可以大大提高查询速度.假如我们创建了一个 mytable表: CREATE TABLE mytable( ID INT NOT NULL, username VARCHAR(16) NOT NULL ); 我们随机向里面插入了10000条记录,其中有一条:5555, admin. 在查找username="admin"的记录…
在数据库表中,对字段建立索引可以大大提高查询速度.假如我们创建了一个 mytable表: ) NOT NULL ); 在查找username="admin"的记录 SELECT * FROM mytable WHERE username='admin';时,如果在username上已经建立了索引,MySQL无须任何扫描,即准确可找到该记录.相反,MySQL会扫描所有记录,即要查询10000条记录. 索引分单列索引和组合索引.单列索引,即一个索引只包含单个列,一个表可以有多个单列索引,但…
原文链接:http://www.cnblogs.com/mailingfeng/archive/2012/09/26/2704344.html 对于任何DBMS,索引都是进行优化的最主要的因素.对于少量的数据,没有合适的索引影响不是很大,但是,当随着数据量的增加,性能会急剧下降.如果对多列进行索引(组合索引),列的顺序非常重要,MySQL仅能对索引最左边的前缀进行有效的查找. 例如:假 设存在组合索引it1c1c2(c1,c2),查询语句select * from t1 where c1=1 a…
