Revise paste Database Sessions

mysql_connect('localhost','user','pass');
mysql_select_db('mydb');

function on_session_start($save_path, $session_name) 
{
  error_log($session_name . ' '. session_id());
}

function on_session_end() 
{
  // Nothing needs to be done in this function
  // since we used persistent connection.
}

function on_session_read($key) 
{
  error_log($key);
  $stmt = 'SELECT session_data FROM sessions ';
  $stmt .= "WHERE session_id='$key' ";
  $stmt .= 'AND unix_timestamp(session_expiration) > unix_timestamp(date_add(now(),interval 1 hour))';
  $sth = mysql_query($stmt);

if($sth)
  {
    $row = mysql_fetch_array($sth);
    return($row['session_data']);
  }
  else
  {
    return $sth;
  }
}
function on_session_write($key, $val) 
{
  error_log("$key = $value");
  $val = addslashes($val);
  $insert_stmt  = "INSERT INTO sessions values('$key', ";
  $insert_stmt .= "'$val',unix_timestamp(date_add(now(), interval 1 hour)))";

$update_stmt  = "UPDATE sessions SET session_data ='$val', ";
  $update_stmt .= "session_expiration = unix_timestamp(date_add(now(), interval 1 hour))";
  $update_stmt .= "WHERE session_id ='$key '";
  
  // First we try to insert, if that doesn't succeed, it means
  // session is already in the table and we try to update
  
  mysql_query($insert_stmt);
  
  $err = mysql_error();
  
  if ($err != 0)
  {
    error_log( mysql_error());
    mysql_query($update_stmt);
  }
}

function on_session_destroy($key) {
  mysql_query("DELETE FROM sessions WHERE session_id = '$key'");
}

function on_session_gc($max_lifetime) 
{
  mysql_query("DELETE FROM sessions WHERE unix_timestamp(session_expiration) < unix_timestamp(now())");
}
  
          
// Set the save handlers
// This will make the session functions/variables use our functions instead.
session_set_save_handler("on_session_start",   "on_session_end",
      "on_session_read",    "on_session_write",
      "on_session_destroy", "on_session_gc");
  
// Carry on as if you were normal
session_start();
?>