Hàm mysqli_multi_query() trong PHP - PHP Function

$con = mysqli_connect("localhost","my_user","my_password","my_db");
// Check connection
if (mysqli_connect_errno()){
	echo "Failed to connect to MySQL: " . mysqli_connect_error();
}

$sql = "SELECT Lastname FROM Persons ORDER BY LastName;";
$sql .= "SELECT Country FROM Customers";

// Execute multi query
if (mysqli_multi_query($con,$sql)){
	do{
	    // Store first result set
	    if ($result=mysqli_store_result($con)) {
	    	// Fetch one and one row
		    while ($row=mysqli_fetch_row($result)){
		        printf("%s
",$row[0]);
		    }
		    // Free result set
		    mysqli_free_result($result);
	    }
    }while (mysqli_next_result($con));
}

mysqli_close($con);