Why my php array is over written when they have same Keys -

i have custom php function executes stored procedure , returns array:

function test(){   $in      = array("abc","bcd","efg");   $result  = mydba->executestoredprocedure('proc1',$in);   $arr_sim = array();    foreach ($result['recordset'] $rows) {     if (!empty($rows)) {       echo $arr_sim[$rows['field1']] = $rows['field2'];     }   }    return $arr_sim; } 

in above function $arr_sim returning number of items correctly when rows["field1"] values different. if rows["field1"] values same overwriting first value , returning last one. how can overcome this?

array ( [chicago] => 'sears', [rochester] => 'liberty' ) 

if $arr_sim contains these items returned correctly. because keys different.

array ( [chicago] => 'mcd', [chicago] => 'tacobell' ) 

if $arr_sim contains these items not returned correctly. because keys same, "chicago".

array keys must unique. instead, this:

// want array // array('chicago' => array('mcd', 'tacobell'));  function test(){   $in  = array("abc","bcd","efg");   $result = mydba->executestoredprocedure('proc1',$in);  $arr_sim=array();  foreach ($result['recordset'] $rows) {   if(!empty($rows)){     if(array_key_exists($rows['field1'], $arr_sim) {         $arr_sim[$rows['field1']][] = $rows['field2'];     } else {         $arr_sim[$rows['field1']] = array($rows['field2']);     }   }  }  return $arr_sim; }