Passing value from ajax to a php variable

hi there,
when we use ajax the value is in server side, which on successfule execution can be shown using

.done(function(data)
{
   console.log(data)
}

The result of the ajax is inside “data”. My question is can we pass the value of “data” in a php variable.

My scenario is :
There is a dropdown, below this is an html table. So when the user selects an item in the dropdown, using ajax the selected values passes in
the “data”.

After this I am running a Mysql query “Select name, age, sex from student where name = ‘{$retvalue}’;

Now instead of “??”, I want to pass value inside “data” in a php variable
“$retvalue”. How can I achieve this.

I have tried my level best and after a thorough search in the net, i am not able to find anything.

Please Help