retrieving values from a database in drupal 7

Question

I am new to drupal. I am trying to create a function that will retrieve rows from a database and display the results.From the tutorials I have read, I am trying to implement a function I have created but no results are displayed. There's just a whitespace. Where might I be going wrong? Here is my code.

function print_users(){
$query = "SELECT first_name, middle_name, last_name FROM {registered_users}";
$header = array(
array('data' => t('Cell 1'), 'field' => 'first_name', 'sort' => 'ASC'),
array('data' => t('Cell 2'), 'field' => 'middle_name'),
array('data' => t('Cell 3'), 'field' => 'last_name'),
);
$q = db_query($query . tablesort_sql($header));
while ($r = db_fetch_array($q)) {
    $rows[] = $r;
}
print theme('table', $header, $rows);

}

and am calling it as follows via a menu link

 $items['view_users'] = array(
        'title' => "view",
        'description' => 'Viewing service',
        'page callback' => "print_users",
        'access callback' => TRUE, 
        'weight' => '2',

);

Answer 1

$select = db_select('registered_users', 'c')
->condition('c.fieldname', $id)  //try the condition if u have anything
->fields('c');

$result = $select->execute();
if($result->rowCount() == 0) return false;

$val = $result->fetch();

for sorting try asc or desc followed by the condition you can get the answer in google itself

Answer 2

The title mentions Drupal 7, but db_fetch_array() no longer exists in 7.x so you want to make sure what version you're actually using, and that you're not wasting your time with tutorials for previous versions.

Also, looking at the last line of your function:

 print theme('table', $header, $rows);

A Drupal function called from the menu does not print directly its HTML output, it must return it as a string, so that the caller combines it with the rest of the page.