Here's a useful function.  
  It logs to the apache error log. 
  When you want to see the errors in the browser add the line below to the script.
  define(DISPLAY_MYSQL_ERRORS,1);
  // ---------------------------------------------------------------------------
  // -- logs to syslog use like this: log_mysql_error($sql,__FILE__,__LINE__);
  // $sql, file and line are optional. __FILE__,__LINE are php magic constants
  // ----------------------------------------------------------------------------
  function log_mysql_error($sql='',$file='',$line=0) {
   global $HTTP_SERVER_VARS;
   $PHP_SELF = $HTTP_SERVER_VARS['PHP_SELF'];
   $msg = "MySQL Says: " . mysql_error();
   error_log($msg,0);
   if (1 == DISPLAY_MYSQL_ERRORS) {
      echo "$msg
\n";
   }
   if (!empty($sql)) {
    $msg="$PHP_SELF: (FILE=$file) (LINE=$line)\n SQL Statement was: $sql";
    error_log($sql,0);
    if (1 == DISPLAY_MYSQL_ERRORS) {
       $msg="$PHP_SELF: (FILE=$file) (LINE=$line)\n
SQL Statement was: $sql";
       echo "$msg\n";
    }
   }
   exit;
  }