SELECT SUM(avg1) FROM (SELECT user_id, AVG(score) as avg1 FROM results GROUP BY user_id)

in this case results table might have multiple records on 1 user id so basically it gets average score of all users and than sums all average number

$arr = ['key0' => 'val0','key1' => 'val1', 'key2' => 'val2', 'key3' => 'val3'];
$removeKeys = ['key1', 'key2', 'key3'];

$arr = array_diff_key($arr, array_flip($removeKeys));

Async/Await

was created to simplify the process of working with and writing chained promises.

Async

functions return a Promise. If the function throws an error, the Promise will be rejected. If the function returns a value, the Promise will be resolved.

Template literal syntax uses dollar sign

$

followed by curly brackets

${expression}

let name = 'George'
let age = 25

document.write(`My name is ${name} and I am ${age} years old!`)

Function declarations are hoisted. It means, we can use the function before we declare it

hoisted(); // logs "foo"

function hoisted() {
  console.log('foo');
}

Function expressions - anonymous functions are not hoisted:

notHoisted(); // TypeError: notHoisted is not a function

var notHoisted = function() {
   console.log('bar');
};

Functions don't need to be defined before they are called. In this example, function

printMe()

is defined after it's called but it works without errors

echo printMe();

function printMe() {
    return 'Print some text';
}

Exception is

conditional function

. In this example function

foo()

will not be defined until the

if ($makefoo)

conditional statement gets executed

$makefoo = true;

/* We can't call foo() from here 
   since it doesn't exist yet,
   but we can call bar() */
// foo();

bar();

if ($makefoo) {
  function foo()
  {
    echo "I don't exist until program execution reaches me.\n";
  }
}

/* Now we can safely call foo()
   since $makefoo evaluated to true */

if ($makefoo) foo();

function bar() 
{
  echo "I exist immediately upon program start.\n";
}

Functions within functions. Function

bar()

will not be defined until the function

foo()

is executed

function foo() 
{
  function bar() 
  {
    echo "I don't exist until foo() is called.\n";
  }
}

/* We can't call bar() yet
   since it doesn't exist. */
// bar();


foo();

/* Now we can call bar(),
   foo()'s processing has
   made it accessible. */

bar();

Note: All functions in PHP have the global scope - they can be called outside a function even if they were defined inside and vice versa

Shows details about each column from

decorations

table including column comments

SHOW FULL COLUMNS FROM decorations

Selects

is_optional

column comment which exists in

decorations

table using

information_schema

database

SELECT COLUMN_COMMENT 
FROM information_schema.COLUMNS 
WHERE TABLE_SCHEMA = 'geiger' 
    AND TABLE_NAME = 'decorations' 
    AND COLUMN_NAME = 'is_optional'

Sets new comment for

name

column in

channels

table

ALTER TABLE `channels` CHANGE `name` `name` varchar(255) COMMENT 'name of channel'