无法使用会话处理程序中定义的连接代码查询MySql表

I use the following connection code in open function of a session handler file named sessionhandler.php for establishing connection between session handler and MySql database named AB, for example.

<---sessionhandler.php--->

function _open()
{

global $db;

$hostname_AB = "localhost";
$database_AB = "database";
$username_AB = "user";
$password_AB = "pass";
$AB = mysql_pconnect($hostname_AB, $username_AB, $password_AB) or trigger_error(mysql_error(),E_USER_ERROR); 
$db = mysql_select_db($database_AB, $AB) or die("Couldn't select database");

    if ($db = mysql_pconnect($hostname_AB, $username_AB, $password_AB))
    {
        return mysql_select_db('sessionhandler', $db);
    }

    return FALSE;
}

function _close()
{
    global $db;

    return mysql_close($db);
}

The problem is that, I can't make query to any other table for example my_table1, my_table2, etc. of AB database using the connection code quoted in the first block above. The first code block only establishes connection between the session handler file sessionhandrer.php & database table sessionhandler only.

In order to make query to other tables of the database AB I had to use seperate connection file that contains the following code:

$hostname_AB = "localhost";
$database_AB = "database";
$username_AB = "user";
$password_AB = "pass";
$AB = mysql_pconnect($hostname_AB, $username_AB, $password_AB) or  
trigger_error(mysql_error(),E_USER_ERROR);

Example of a query using above connection code that ignores the connection code of sessionhandler.php :

mysql_select_db($database_AB, $AB);
$query_test = "SELECT users.id, users.name FROM users WHERE users.id = >= 1";
$test = mysql_query($query_test, $AB) or die (mysql_error());
$row_test = mysql_fetch_assoc($test);
$totalRows_test = mysql_num_rows($test);

Absence of the above connection file causes typical MySql connection error in case there are any queries there from other tables of AB database.

How shall I combine these two connection files for making queries to all tables of database AB?

Though I haven't had time to merge these two connection queries into one, mathematical logic says that

if ($db = mysql_pconnect($hostname_AB, $username_AB, $password_AB))
{
return mysql_select_db('sessionhandler', $db);
}

the above block of equation confines the database connection to a single table sessionhandler and primarily that's why query to other tables using this connection code is invalid.