Form api - tableselect selected value

function db_showtable_form($form,&$form_states)
{
...
$form['db_showtable']['selected'] = array(
    '#type' => 'tableselect', 
    '#header' => $header,
    '#options' => $options,
    '#empty' => t('A tábla üres.'),
    '#multiple' => FALSE,
    '#js_select' =>TRUE,
);
 
$form['db_showtable']['add'] = array(
    '#type' => 'submit',
    '#value' => t('Új sor'),
    '#submit' => array('db_new_row_prepare'),
);
 
}