php - Using ajax with mysql to validate before rendering -

i pretty new ajax might ask might simple of you.

i looking best way check user posting checkdata.php verily price in database.

i have long database works find need validation.

product

pid      name                  size     price   1        chocolate              12        30.00 

i have form , in form posting pid name , size

in pdo statement doing this

select pid, price, name, size product pid=:pid , size=:size , name=:name 

this works fine.

but want use ajax check user same whats in database , equal same price in database.

if not same should have alert message saying "don't mess code."

i have long table. sorry cant show code long

in table have name echo database

size dropdown list

and pid hidden input.

i have jquery

$(document).ready(function(){     $('#selected').hide();     $('#button').click(function(){         var pid = $('#pid').val();         var size = $('#size').val();         var qty = $('#qty').val();         var price = '\u00a3' + parseint($('#pricetag').text().replace(/^\d/, ''), 10) * qty;         var size = $('#size').val();         if (!/^[1-9]\d?$/.test(qty)){             alert('quantity should not below 1 or null');             return false; // don't continue         }          else {         $('#sprice').text(price);         $('#ssize').text(size);         $('#selected').slidedown();         }         $.ajax({             url: 'checkdata.php',             type: 'post',             data: { pid:pid, size:size, qty:qty},             success: function(data)             {              }         });     }); });  <?php session_start()  if(isset($_post['pid']) && isset($_post['size']) && isset($_post['qty']) && isset($_post['name'])){        $pid = $_post['pid'];     $size = $_post["size"];     $qty = $_post['qty'];     $name= $_post['name'];  . . .   somewhere in php tag have statement right price based on data getting posted    select pid, price, name, size product pid=:pid , size=:size , name=:name  ?> 

summary how can use ajax check getting posted same on database before render page.

you shouldn't round-tripping prices through client anyways. it's 1 thing pull price , display user, should never accept price value user. fetch fresh copy database when comes time calculate costs.

if want "fix" price if item in shopping cart prolonged duration, , you're changing prices in database, keep price in user's session. that's purely server-side data structure, , can't meddled directly.

that'd let things "item price has changed since added cart. accept new updated price or remove cart?".