php - Warning: Invalid argument supplied for foreach() when retrieving data from database -

i attempting retrieve data 2 tables , echo results out, sql appears correct tells argument invalid. heres code:

// retrieve information related post     function get_post_data($post_id){          //test connection         try{             //connect database             $dbh = new pdo("mysql:host=localhost;dbname=mjbox","root", "usbw");         //if there error catch here         } catch( pdoexception $e ) {             //display error             echo $e->getmessage();         }          $sql = 'select * mjbox_images join mjbox_posts using (post_id) post_id = $post_id';         $result = $dbh->query( $sql );          foreach($result $row):              echo $row['img_id'];          endforeach;      } 

the $post_id in query won't being expanded because string single quoted.

it should work better with:

$sql = "select * mjbox_images join mjbox_posts using (post_id) post_id = $post_id"; 

or:

$sql = 'select * mjbox_images join mjbox_posts using (post_id) post_id = '.$post_id;