function getclientstock($client) {


$option=array();
$option['driver']   = 'mysql';            // Database driver name
$option['host']     = 'localhost';    // Database host name
$option['user']     = 'user';       // User for database authentication
$option['password'] = 'pass';   // Password for database authentication
$option['database'] = 'database';      // Database name
$option['prefix']   = '';             // Database prefix (may be empty)
$db=JDatabaseDriver::getInstance($option);

    $query=$db->getQuery(true);
    $query->select($db->quoteName(array('unit_imei' , 'client')));
    $query->from($db->quoteName('connections'));
    $query->where($db->quoteName('client') . ' = ' . $db->quote($client));
    $db->setQuery($query);
    $result=$db->loadAssocList();
    return $result;
};

<?php
    $option=array();
    $option['driver']   = 'mysql';            // Database driver name
    $option['host']     = 'localhost';    // Database host name
    $option['user']     = 'user';       // User for database authentication
    $option['password'] = 'pass';   // Password for database authentication
    $option['database'] = 'database';      // Database name
    $option['prefix']   = '';             // Database prefix (may be empty)
    $db=JDatabaseDriver::getInstance($option);

    function getclientstock($db, $client) {

        $query=$db->getQuery(true);
        $query->select($db->quoteName(array('unit_imei' , 'client')));
        $query->from($db->quoteName('connections'));
        $query->where($db->quoteName('client') . ' = ' . $db->quote($client));
        $db->setQuery($query);
        $result=$db->loadAssocList();
        return $result;
    };

    function setclientstock($db, $client) {
      // code here...

    };

?>