$("#DEL").click(function(){
    $("table tr input:checked").parents('tr').remove();
});

$("#DEL").click(function(){
    var checked = $("table tr input:checked").size();
    var total = $("table tr").size();
    if (checked < total) {
        $("table tr input:checked").parents('tr').remove();
    } else {
        alert("You cannot delete all rows!");
    }
});

$("#DEL").click(function () {
    console.log($("table tr input:checked").length)
    if ($("table tr").length === 1
       || $("table input:checked").length === $("table tr").length) {
        alert("cannot delete last tr")
    } else {
        $("table tr input:checked").parents('tr').remove();
    }
  });

$("table tr:not(:first) input:checked").parents('tr').remove();

alert("Sorry, cannot delete all rows");