Implode array in php mysql_fetch_array -

i cannot solve seeming simple problem. have following simple code , want echo result of $atl5_alert_query , separated comma (,):

$atl5_alert_query = mysql_query("select `mobile` `dbo_tech_name` `alertlevel`= 1");   $dataset = array();  while ($data = mysql_fetch_array($atl5_alert_query))  {    $dataset[] = $data;  } echo implode (",", $dataset); 

however, i'm getting "notice: array string conversion "...

in code $data array well, $dataset becomes array of arrays, cannot concatenate. should searched value this:

while ($data = mysql_fetch_array($atl5_alert_query)) {    $dataset[] = $data['mobile']; } 

or:

while ($data = mysql_fetch_array($atl5_alert_query)) {    $dataset[] = $data[0]; } 

or:

while ($data = mysql_fetch_assoc($atl5_alert_query)) {    $dataset[] = $data['mobile']; } 

if cannot change this, , have $dataset array, can implode that:

echo implode(',', array_map(function($a){   return $a['mobile']; },$dataset));