通过SQL动态更改下拉列表并计算总和？

I've got a row in a table with 3 fields laid out as so:

Job            Pay Grade       Cost
<Select>       <Select>        <Calculation>

I've got an SQL table with the information above in it, for example:

Job            Pay Grade       Cost
Techie         1               100
Techie         2               200
Engi           2               300
Engi           3               400
Engi           4               500

What I need to do is to be able to select a Job from the dropdown and then the Pay Grade select box will change depending on what matches that job in the SQL database. It will then show the cost which relates to the to selected.

How can I go about this as I am a little stuck

You need to post the select job via $.ajax and then in success function populate the dropdown list like this:

function selectHandler (event, ui)
        {
        var id = event.target.id;
        $.ajax({
                type: "POST",
                url: "/php/get_quantity_type.php",
                dataType:"json",
                data: { ingridient : ui.item.value},
                success: function(data){$("#"+id+"_t").empty(); $.each(data,function(index,value) {$("#"+id+"_t").append('<option value="' + value + '">' + value + '</option>');})}
                });
        } 

This example takes a name of a material from select list posts it via $ajax() to a php script and writes it down to a new dropdown list which id is based on id that triggered the event. If you need the php code just ask:)

You bind your job list to the event handler above:

("#job_list").bind("select",selectHandler);

This code posts data to "/php/get_quantity_type.php", and passess the result to function declared in success attribute;

First create ajax request when a job title is selected. WIthin the success callback of the request will generate html for the options for pay grade select from JSON response from server

jQuery

$('select.jobTitle').change(function(){
    var $titleSelect=$(this);
    $.getJSON('processJobGrades.php', { jobTitle : $(this).val() }, function(response){
        var gradesOptionsHtml=''; 
        /* create options html from json response */
        $.each( response, function(i, item){
            gradesOptionsHtml+='<option value="'+item.grade+' data-cost="'+item.cost+'">'+item.grade+'</option>';
        });  
         $titleSelect.parent().find('select.jobGrade').html(gradesOptionsHtml);       
    });   
});

IN processJobGrades.php receive $_GET['jobTitle'] . Do DB lookup and create json to send back.

PHP

$outputArray=array();

/*in loop over DB data:*/
$outputArray[]= array( 'grade'=>$row['grade'], 'cost'=>$row['cost']);

/*Output final array as JSON*/
echo json_encode( $outputArray);

jQuery change handler for paygrade select to get cost

$('select.jobGrade').change(function(){
     var cost=$(this).find(':selected').data('cost')
     $(this).parent().find('input.jobCost').val( cost);
})