MySQL Forums :: PHP :: Passing dropdown list value to another SELECT statement on same page

Supposing there are two tables, parent (PK pid, ...) and child (PK cid, FK pid, ...), then at the top you have something like ...

if( isset( $_GET['pid'] )) { 
  $pid = $_GET['pid']; 
  if( $pid != $_SESSION['pid'] ) unset( $_SESSION['cid'] ); 
  $_SESSION['pid'] = $pid; 
} 
elseif( isset( $_SESSION['pid'] )) { 
  $pid = $_SESSION['pid']; 
} 
if( isset( $_GET['cid'] )) { 
  $cid = $_GET['cid']; 
  $_SESSION['cid'] = $cid; 
} 
elseif( isset( $_SESSION['table'] )) { 
  $table = $_SESSION['table']; 
}

Then further down, the query for child rows matching the pid selected by the user in the parent dropdown is...

select ... from child where pid=$pid;