我需要使用mysql_close（连接）吗？

I have the following code in db.php to connect to my DB.

<?php
$DB_HOST        = "localhost";
$DB_NAME        = "db";
$DB_USER        = "user";
$DB_PASSWORD        = "pass";

$con = mysql_connect($DB_HOST, $DB_USER, $DB_PASSWORD);

if (!$con)
{
  die('Could not connect: ' . mysql_error());
}

mysql_select_db($DB_NAME , $con);
?>

In my other script I include it using:

include("db.php");

In some cases I receive the ff error:

[10-Mar-2012 10:47:20] PHP Warning: mysql_connect() [function.mysql-connect]: User db_user already has more than 'max_user_connections' active connections in /home/user/public_html/sc/db.php on line 8

Now, I am wondering if I need to close the connection like:

<?php
include("db.php");

//other stuff here

mysql_close($con);
?>

BTW, I have a value of 100 max_connections in my MySQL config.

I also research about persistent connection and I believe my code above is not a persistent connection.

No, this won't help you if you close it at the end of the script. mysql_close() is just useful in case you want to free up resources before you end your script, because your connection is closed as soon as execution of the script ends

If you don't close your connections, they will stay open and take up precious resources on the server. I guess there's there the security point too, you don't want to risk someone getting a hold of the connection.
I prefer to put my database in a class and use __construct to create the connection, and __destruct to close the connection. If your unfamiliar with classes. The __construct and __destruct gets called automatically when you create and destroy a class.

Edit:
There was originally meant to be an example. But I have a basic but working mysql class here https://stackoverflow.com/a/9651249/1246494.

It shows the usage of mysql_close and how I was trying to relate it to the class destructor. The point was, any network connection should be closed, whether your database is on a remote server, or localhost.