How to Implement Pagination with Random Ordering in PHP and MySQL?

PHP MySQL Pagination with Random Ordering

When implementing search functionality with pagination on a website, it is crucial to address issues related to the random ordering of results. This article provides solutions to the following challenges:

1. Excluding previously seen results on subsequent pages:
   To prevent already viewed results from reappearing, a memory-efficient solution is to use a technique called pagination with exclusion list. This involves storing the IDs of the displayed results in a session or database and excluding them from subsequent queries.
2. Ensuring different sets of results on the first page:
   To guarantee a unique set of results on the first page, you can utilize the RAND() function with a constant seed value. By changing this seed value after each visit, you can ensure a fresh ordering without compromising random sorting.
3. Practical implementation of seed value:
   In MySQL, you can use the RAND(SEED) function, where SEED is a user-specified integer. By setting the seed to a different value each time the user visits the first page, you can achieve randomized yet distinct ordering.

Example:

<code class="php"><?php
session_start();

// Generate a unique seed value for the first page
if (!isset($_SESSION['seed'])) {
    $_SESSION['seed'] = rand(1, 1000);
}

// Exclude previously seen results
$excludedIds = array();
if (isset($_SESSION['seenResults'])) {
    $excludedIds = $_SESSION['seenResults'];
}

// Query with random ordering and exclusion
$query = "SELECT * FROM table WHERE id NOT IN ('" . implode("', '", $excludedIds) . "') ORDER BY RAND(" . $_SESSION['seed'] . ") LIMIT 10";</code>

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