Ajax :: Using To Implement Php Inside Of Loop?

I have a theoretical question, I can't really post my code. But I have four results from reads to a database using php. I then read from an xml file using javascript using a loop. I am basically creating a chart of four variables with several different values for each variable. Some of the values for each variables come from the database using php, and some come straight off the XML file parsing done by the javascript. I initially had the php fetch/extract inside of the javascript loop, but it only assigned the first variables values to all the other variables. I discovered (after hours of googling) the difference between client side and server side code. So, after all this typing, my question is where should I look for tutorials on using Ajax to be able to use php code inside of a javascript loop? (If at all possible)