Monday, January 7, 2019

PHP : In PHP 5, what is the difference between using self and $this?

Short Answer

Use $this to refer to the current object. Use self to refer to the current class. In other words, use $this->member for non-static members, use self::$member for static members.

Full Answer

Here is an example of correct usage of $this and self for non-static and static member variables:

<?php
class X {
    private $non_static_member = 1;
    private static $static_member = 2;

    function __construct() {
        echo $this->non_static_member . ' '
           . self::$static_member;
    }
}

new X();
?>

Here is an example of incorrect usage of $this and self for non-static and static member variables:

<?php
class X {
    private $non_static_member = 1;
    private static $static_member = 2;

    function __construct() {
        echo self::$non_static_member . ' '
           . $this->static_member;
    }
}

new X();
?>

Here is an example of polymorphism with $this for member functions:

<?php
class X {
    function foo() {
        echo 'X::foo()';
    }

    function bar() {
        $this->foo();
    }
}

class Y extends X {
    function foo() {
        echo 'Y::foo()';
    }
}

$x = new Y();
$x->bar();
?>

Here is an example of suppressing polymorphic behaviour by using self for member functions:

<?php
class X {
    function foo() {
        echo 'X::foo()';
    }

    function bar() {
        self::foo();
    }
}

class Y extends X {
    function foo() {
        echo 'Y::foo()';
    }
}

$x = new Y();
$x->bar();
?>

The idea is that $this->foo() calls the foo() member function of whatever is the exact type of the current object. If the object is of type X, it thus calls X::foo(). If the object is of type Y, it calls Y::foo(). But with self::foo(), X::foo() is always called.

https://stackoverflow.com/questions/151969/when-to-use-self-over-this

Monday, December 24, 2018

sql : MYSQL Update Statement Inner Join Tables

https://stackoverflow.com/questions/8057565/mysql-update-statement-inner-join-tables

Wednesday, December 19, 2018

SQL | Join (Cartesian Join & Self Join)

CARTESIAN JOIN: The CARTESIAN JOIN is also known as CROSS JOIN. In a CARTESIAN JOIN there is a join for each row of one table to every row of another table. This usually happens when the matching column or WHERE condition is not specified.

In the absence of a WHERE condition the CARTESIAN JOIN will behave like a CARTESIAN PRODUCT . i.e., the number of rows in the result-set is the product of the number of rows of the two tables.
In the presence of WHERE condition this JOIN will function like a INNER JOIN.
Generally speaking, Cross join is similar to an inner join where the join-condition will always evaluate to True

Syntax:

SELECT table1.column1 , table1.column2, table2.column1...
FROM table1
CROSS JOIN table2;


table1: First table.
table2: Second table

https://www.geeksforgeeks.org/sql-join-cartesian-join-self-join/

Monday, December 17, 2018

PHP: Create Pagination in PHP, MYSQL, JQUERY and AJAX

https://www.skptricks.com/2018/01/create-pagination-in-php-mysql-jquery-and-ajax.html

PHP : DataTables - Server-side Processing using php and Ajax

https://github.com/sokchab/phpserverside

PHP: Simple pagination

<!DOCTYPE html>
	<html lang="en">
	<head>
	<meta charset="UTF-8">
	<title>Pagination</title>
	</head>
	<body>
	<?php
	// connect to database
	$con = mysqli_connect('localhost','root','');
	mysqli_select_db($con, 'pagination');

	// define how many results you want per page
	$results_per_page = 10;

	// find out the number of results stored in database
	$sql='SELECT * FROM alphabet';
	$result = mysqli_query($con, $sql);
	$number_of_results = mysqli_num_rows($result);

	// determine number of total pages available
	$number_of_pages = ceil($number_of_results/$results_per_page);

	// determine which page number visitor is currently on
	if (!isset($_GET['page'])) {
	$page = 1;
	} else {
	$page = $_GET['page'];
	}

	// determine the sql LIMIT starting number for the results on the displaying page
	$this_page_first_result = ($page-1)*$results_per_page;

	// retrieve selected results from database and display them on page
	$sql='SELECT * FROM alphabet LIMIT ' . $this_page_first_result . ',' . $results_per_page;
	$result = mysqli_query($con, $sql);

	while($row = mysqli_fetch_array($result)) {
	echo $row['id'] . ' ' . $row['alphabet']. '<br>';
	}

	// display the links to the pages
	for ($page=1;$page<=$number_of_pages;$page++) {
	echo '<a href="index.php?page=' . $page . '">' . $page . '</a> ';
	}

	?>
	</body>
	</html>

Mehedi Hasan's BLog