How to Display Unique Values from database using db_select in Drupal

Question

i tried with following code but i cant get the attached output

$query = db_select('webform_submitted_data', 'u');
$query->fields('u', array('sid','nid','data'));
$query->condition('nid','49','=');
$results =$query->execute();

echo "<table>";
echo "<tr>";
echo "<th>Name <th>";
echo "<th>Post <th>";
echo "</tr>";
while($record = $results->fetchAssoc())
{
 $sid = $record['sid'];
 $nid = $record['nid'];
$submission = webform_get_submission($nid,$sid);
echo "<tr>";
echo $submission->data[1][0];
echo $submission->data[2][0];
echo "</tr>";
}
echo "</table>";
}

Answer 1

Try

$query = db_select('webform_submitted_data', 'u');
$query->fields('u', array('sid','nid')); $query->condition('nid','49','=');
$results =$query->distinct()->execute();

Api info about unique

Answer 2

If you use this query then, its provide proper distinct query.

<?php  

$select = db_select('service_payment_transaction','o');
$select->distinct('o.transaction_id');
$select->innerJoin('users', 'u', 'u.uid = o.user_id');
$select->fields('o');
$select->fields('u');
$select->condition('o.service_gv_code','','!=');
$select->range($start,$page_count);
$select->groupBy('o.service_gv_code');

$select->orderBy('transaction_id', 'DESC'); $result_query = $select->execute();