SOURCE

$(document).ready(function () {
    var sk = "123,577,890";
    var st="ab,cc,dd";

    $('#mySelect').change(function () {
        var selectedIndex = $(this).prop('selectedIndex');
        var selectedValue = sk.split(',')[selectedIndex];
        var selectedValue2 = st.split(',')[selectedIndex];
        if(selectedValue){
            $('#result').text(selectedValue+','+selectedValue2);
        }else{
            $('#result').text('');
        }
        
    });
});

<select id="mySelect" style="width:200px;line-height:2;">
  <option value="1">ykm</option>
  <option value="2">tko</option>
  <option value="3">test</option>
</select>
<div id="result"></div>