What is the purpose of using left join queries in PHP?

Left join queries in PHP are used to retrieve data from two or more tables based on a related column between them. The purpose of using a left join is to retrieve all records from the left table (the table mentioned first in the query) along with matching records from the right table. If there are no matching records in the right table, NULL values are returned. 

// Example of using a left join query in PHP
$servername = "localhost";
$username = "username";
$password = "password";
$dbname = "myDB";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

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

// SQL query with left join
$sql = "SELECT users.id, users.name, orders.order_id FROM users LEFT JOIN orders ON users.id = orders.user_id";

$result = $conn->query($sql);

if ($result->num_rows > 0) {
    // Output data of each row
    while($row = $result->fetch_assoc()) {
        echo "User ID: " . $row["id"]. " - Name: " . $row["name"]. " - Order ID: " . $row["order_id"]. "<br>";
    }
} else {
    echo "0 results";
}

$conn->close();

Keywords

PHP left join SQL query database data retrieval

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