Multi layer architecture


SQL
	ACID properties
		Atomic -- The transaction runs completely or not at all
		Consistent -- Each transaction moves from one consistent state to another
		Independent -- Every transaction runs as if it were the only one on the system
		Durable -- Data changes survive hardware and software failure.
	Abort 
	Table vs database
	create table
		schema
		not null
		primary key
	types
		decimal(5,2)
		date and time types
		enum
		blob/longblob
	update tablename set columnname = value where ...
	delete from tablename where ...
	select columnname from tablename where .. order by columname limit 3
	(not in 2020)alter table ...
	drop tablename
	describe table tablename
	joins
	nested queries (and in vs =)
	min and max count and average and group by
	insert into tablename values ( ...)
	(not in 2022)database decomposition
		might cost speed
		reduces redundency and possibility of inconsistency
	Indexes

	
PHP
	Built in arrays
		$_GET
		$_POST
		$_COOKIE
		$_SESSION
		$_REQUEST
	Error supression with @
	isset($varname)
	empty($varname)	
	Error checking with die
	Arrays
		Not really arrays
		indexed by key, which can be string
		not always the same type
		foreach ($array as $item)
		foreach($array as %key => $item)
	Cookies
		Uses
		session cookies vs cookies with an expire time
		limits on size
		limits on domain/hostname
		Can be turned off
		$_COOKIE
	Session variables
		$_SESSION
		Needs cookies
		No reasonable size limits
		Expires when the session does
		Allows for privacy
		Requires cookies
	Loops
		while loops
		for loops
		foreach($array as $value)
		foreach($array as $index => $value)
	Functions
		default arguments
		function foo($name = "Default Name")
	(not much in 2022) Objects
		__construct
		__tostring
		$this->thing
		$this->method() vs method()
		class vs local vs global variables
	print_r
	header("location: ...")	
	Variables
		global
		superglobal
			$_REQUEST
			$_COOKIE
			$_POST
			$_GET
	Databases
		Know some way to fetch data like
		http://euclid.nmu.edu/~rappleto/Classes/CS465/PHP/Databases/Database_Example_Object.php.txt
		real_escape_string
		Error checking

	Files (not in 2022)
		Open a file
		Read a file
		Write a file
		See if the file exists
	File Uploads
		See https://www.php.net/manual/en/features.file-upload.post-method.php

Login
	To login:
		Get username/pwd
		if you like it
			Server sends random number to client

	To verify you are logged in:
		client sends chosen number back to server with request (like an input field or cookie)

	Remember...
		passwords always hashed in the DB

	Remember, Session variables work better than this because they are this.