UPDATE table_name
    SET good_high = $tgh
      , critical_low = $tcl
      , warning_low = $twl
      , warning_high = $twh
    WHERE   user = ?
        AND name = '$threshold_name'
        AND (   good_high <> $tgh
            OR  critical_low <> $tcl
            OR  warning_low <> $twl
            OR  warning_high <> $twh )