我如何关闭mysqi_connection？为什么这很重要？

Question

我怎么能在这里关闭mysqli_connection？为什么关闭连接很重要？

include("mysql.inc.php");

$ID = $_GET["ID"];

$q=mysqli_query($link,"select * from messages Where ID = '$ID'  ORDER BY createID ASC LIMIT 1");

while($e=mysqli_fetch_assoc($q))
$output[]=$e;

print(json_encode($output));