history | 易学教程

Where does the practice “exists (select 1 from …)” come from?

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问题 The overwhelming majority of people support my own view that there is no difference between the following statements: SELECT * FROM tableA WHERE EXISTS (SELECT * FROM tableB WHERE tableA.x = tableB.y) SELECT * FROM tableA WHERE EXISTS (SELECT y FROM tableB WHERE tableA.x = tableB.y) SELECT * FROM tableA WHERE EXISTS (SELECT 1 FROM tableB WHERE tableA.x = tableB.y) SELECT * FROM tableA WHERE EXISTS (SELECT NULL FROM tableB WHERE tableA.x = tableB.y) Yet today I came face-to-face with the

What is the origin of foo and bar? [closed]

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问题 Closed . This question needs to be more focused. It is not currently accepting answers. Closed 6 years ago . Locked . This question and its answers are locked because the question is off-topic but has historical significance. It is not currently accepting new answers or interactions. Where did they come from and when were they first used? 回答1: tl;dr "Foo" and "bar" as metasyntactic variables were popularised by MIT and DEC, the first references are in work on LISP and PDP-1 and Project MAC

Is one's complement a real-world issue, or just a historical one?

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问题 Another question asked about determining odd/evenness in C, and the idiomatic (x & 1) approach was correctly flagged as broken for one's complement-based systems, which the C standard allows for. Do systems really exist in the 'real world' outside of computer museums? I've been coding since the 1970's and I'm pretty sure I've never met such a beast. Is anyone actually developing or testing code for such a system? And, if not, should we worry about such things or should we put them into Room

How to detect the pressed button and display it on Another View? Objective-C

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问题 I am new to iOS app development. I want to create a Calculator App in iOS that has split view. The left side is the "History" Feature in Scroll View and the right side is the calculator itself. Now, regarding the History feature of this app, I am thinking that my program needs to recognize what has been pressed and display it on the Scroll View when the Equal (=) button is pressed. Do you have any idea how will this go on Objective-C? I am using XCode 4.5 and iPhone Simulator 6.0. Thanks in

How to detect the pressed button and display it on Another View? Objective-C

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How to get only unique commits in git

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问题 I want to get list of unique commits in all branches, but if somebody is using rebase in branch commits loose parents. How to solve this problem? How to get list of commits that made unique changes? 回答1: I use git log --oneline --graph --cherry-pick --left-right The operative verb you are looking for is --cherry-pick: --cherry-pick Omit any commit that introduces the same change as another commit on the "other side" when the set of commits are limited with symmetric difference. For example,

C# google contact api deleted contact

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问题 currently I´m writing on a outlook plugin for syncing goolge contacts with outlook but I have to cover some special case: When a contact gets deleted on google side, my application detects the missing contact and creates a new contact based on the contact info from the outlook one. Is there a way to get an event or history from google that tells me a user deleted this contact(s)? Edit 1: Here is my code how I´m accessing the contacts (what is working FINE): public GoogleAccessor() { var

发展简史jQuery时间轴特效

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发展简史jQuery时间轴特效。这是一款鼠标滚动到一定的高度动画显示企业发展时间轴特效。效果图如下：在线预览源码下载实现的代码。 html代码： <div class="wrapper"> <div class="history"> <div class="start-history"> 发展简史 PHYLOGENY <div class="history_left"> 2006 10 月 开展基于互联网的视频服务业务 CC视频联盟正式公测 2008 <span class="history_l

Internet History,Technology,and Security -Security: Encrypting and Signing（Week8）

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Week 8 Security: Encrypting and Signing This week we start two weeks of Internet Security. It is a little technical but don't worry - we stay at a very high level and I am confident that if you are still keeping up with the class that you will enjoy these next two weeks. You won't know enough to be an expert - but many of the security issues that you read about going forward will make a lot more sense to you. The topics we’re covering are encrypting and signing. Using simple examples, we examine how to shield data from prying eyes and make sure that the data was not altered while in transit.

React-Router v4 history on express server

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问题 I have a react app using the following for router history. import { BrowserRouter, Route, Link } from "react-router-dom"; import { createBrowserHistory } from "history"; <BrowserRouter history={history}> ... This is served using Express server like this (server.js)... //for build // Serve the static files from the React app app.use(express.static(path.join(__dirname, 'build'))); app.get('/*', function (req, res) { res.sendFile(path.join(__dirname, 'build', 'index.html')); }); This is working