dropdown list that refresh a div content upon select

dropdown list that refresh a div content upon select

i have totally no idea about how to do this, so i'm gonna just ask away.
I have a dropdown menu which list dates say
1/2/2013
2/2/2013
3/2/2013
4/2/2013
5/2/2013
6/2/2013
7/2/2013
if you were to select one of the dates, a div will pop out with say 5 choices
A
B
C
D
E
each choices are stored in the database, and if say B item is not
available on 2/2/2013, i would have a script to disable it being selected.
I've figured how to create that in php, but my ultimate question is
how do you select any of the dates but yet still able to retrieve the 5
choices from a database?
I'm currently doing something like this
function TheDisabler($aa)
{
global $con, $vdate;
$myresult = mysqli_query($con,"SELECT * FROM burger WHERE timeslot =
'$aa' AND date = '$vdate'");
list($mycount) = mysqli_fetch_row($myresult);
if($mycount >= 1) {
echo "disabled";
}
}
but i figured that this works only once and if i were to change the date,
the items within the div will not change =/