What is the significance of using JOIN in a MySQL query in PHP?

Using JOIN in a MySQL query in PHP allows you to combine rows from two or more tables based on a related column between them. This is useful when you need to retrieve data from multiple tables that are related to each other. By using JOIN, you can avoid making multiple queries and efficiently fetch the required data in a single query. 

<?php
// Establish a connection to the database
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "database";
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

// Query using JOIN to retrieve data from multiple related tables
$sql = "SELECT users.username, orders.order_id FROM users
        JOIN orders ON users.user_id = orders.user_id";
$result = $conn->query($sql);

// Output the data
if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "Username: " . $row["username"]. " - Order ID: " . $row["order_id"]. "<br>";
    }
} else {
    echo "0 results";
}

// Close the connection
$conn->close();
?>

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