KaFai kafaichoi

Why do they call it a relational database? Relational database are usually consisted of different tables which are related to other table by foreign key. And Foreign key in one table is the primary key of a record in another table. We can easily make a query base on different criteria on different table by joining the table.

2.What is SQL? SQL stands for Structured Query Language. It is a Domain Specific Language for managing data in RDBMS

There are two predominant views into a relational database. What are they, and how are they different? They are the data and schema views. Data view displays like a spreadsheet. A schema view descripts the column names and the value type of each column.
In a table, what do we call the column that serves as the main identifier for a row of data? We're looking for the general database term, not the column name.

TL;DR

Install Postgres 9.5, and then:

sudo pg_dropcluster 9.5 main --stop
sudo pg_upgradecluster 9.3 main
sudo pg_dropcluster 9.3 main

Command Line

	Quiz: Lesson 3

	1. What's the difference between rendering and redirecting? What's the impact with regards to instance variables, view templates?
	They both complete a request but redirect will tell the client (browser) to send a brand-new request to a new URL. Therefore, no instance variable from previous action triggering the redirect will be available to the redirected view template . For rendering, the instance variable from the action will be avaiable for the view template being rendered.


	2. If I need to display a message on the view template, and I'm redirecting, what's the easiest way to accomplish this?
	flash[:notice]

	3.If I need to display a message on the view template, and I'm rendering, what's the easiest way to accomplish this?


	<p>This is deprecated, in future versions you may need to <code>bundle binstub rails</code> to work around a system/bundle conflict.<br>
	/home/kafai/.rvm/gems/ruby-2.0.0-p481/gems/paratrooper-0.0.1/lib/paratrooper.rb:1:in <code>require': cannot load such file -- heroku (LoadError)<br>
	from /home/kafai/.rvm/gems/ruby-2.0.0-p481/gems/paratrooper-0.0.1/lib/paratrooper.rb:1:in</code>'<br>
	from /home/kafai/.rvm/gems/ruby-2.0.0-p481@global/gems/bundler-1.6.2/lib/bundler/runtime.rb:76:in <code>require'<br>
	from /home/kafai/.rvm/gems/ruby-2.0.0-p481@global/gems/bundler-1.6.2/lib/bundler/runtime.rb:76:in</code>block (2 levels) in require'<br>
	from /home/kafai/.rvm/gems/ruby-2.0.0-p481@global/gems/bundler-1.6.2/lib/bundler/runtime.rb:72:in <code>each'<br>
	from /home/kafai/.rvm/gems/ruby-2.0.0-p481@global/gems/bundler-1.6.2/lib/bundler/runtime.rb:72:in</code>block in require'<br>
	from /home/kafai/.rvm/gems/ruby-2.0.0-p481@global/gems/bundler-1.6.2/lib/bundler/runtime.rb:61:in <code>each'<br>

	Register in HockeyApp
	-Android
	1. cordova build --release android
	2. keytool -genkey -v -keystore my-release-key.keystore -alias alias_name -keyalg RSA -keysize 2048 -validity 10000
	3. jarsigner -verbose -sigalg SHA1withRSA -digestalg SHA1 -keystore my-release-key.keystore HelloWorld-release-unsigned.apk alias_name
	4. zipalign -v 4 HelloWorld-release-unsigned.apk HelloWorld.apk
	5. upload apk file to HockeyApp

	-IOS
	1. cordova build --release ios

	CREATE TABLE shake_magnitudes (
	event_id int,
	user_id int,
	recorded_at timestamp,
	magnitude float,
	PRIMARY KEY (event_id, user_id, recorded_at)
	)
	WITH CLUSTERING ORDER BY (user_id ASC, recorded_at ASC);

	:e. :edit . at current working directory
	:sp. :split . in split at current working directory
	:vs. :vsplit . in vertical split at current working directory
	:E :Explore at directory of current file
	:Se :Sexplore in split at directory of current file
	:Vex :Vexplore in vertical split at directory of current file

	% create a new file
	d create a new directory
	R rename the file/directory under the cursor

	#!/bin/bash
	# installing erlang on ubuntu's

	VERSION="R15B01"

	sudo apt-get install build-essential libncurses5-dev openssl libssl-dev

	sudo mkdir -p /opt/erlang/
	curl -O https://raw.github.com/spawngrid/kerl/master/kerl && chmod a+x kerl
	sudo mv kerl /opt/erlang/