PHP MySQL - ORDER BY

When working with large amounts of data in a MySQL database, it is often necessary to sort the results in a specific order. This can be done using the ORDER BY clause in a SQL query.

In PHP, MySQL queries can be executed using the mysqli extension or PDO. Both extensions support the ORDER BY clause.

The syntax for the ORDER BY clause is:

SELECT column1, column2, ...
FROM table_name
ORDER BY column1, column2, ... ASC|DESC;

• column1, column2, ...: The columns to sort by.
• table_name: The name of the table to select from.
• ASC|DESC: Optional. Specifies the order of sorting, either ascending (ASC) or descending (DESC).

Here is an example PHP script using mysqli to sort a list of books by their title:

<?php
// Connect to database
$mysqli = new mysqli("localhost", "username", "password", "library");

// Prepare query
$query = "SELECT title, author, year_published FROM books ORDER BY title ASC";

// Execute query
$result = $mysqli->query($query);

// Print results
while ($row = $result->fetch_assoc()) {
    echo $row["title"] . " by " . $row["author"] . " (" . $row["year_published"] . ")\n";
}

// Close connection
$mysqli->close();
?>

Here is an example PHP script using PDO to sort a list of users by their age:

<?php
// Connect to database
$pdo = new PDO("mysql:host=localhost;dbname=mydatabase", "username", "password");

// Prepare query
$query = "SELECT name, age FROM users ORDER BY age DESC";

// Execute query
$result = $pdo->query($query);

// Print results
while ($row = $result->fetch()) {
    echo $row["name"] . " is " . $row["age"] . " years old\n";
}

// Close connection
$pdo = null;
?>

In both examples, the ORDER BY clause is used to sort the results in either ascending or descending order. The results are then printed to the screen using a while loop.

It is important to note that when using the ORDER BY clause, the database server will sort the entire result set before returning it. This can have an impact on performance for large result sets.

In conclusion, the ORDER BY clause is an essential part of SQL queries when working with large amounts of data. It allows for the sorting of results in a specific order and can be used with both mysqli and PDO in PHP.