Question

I’m learning Php & Mysql.

I’ve a database(practice) with 2 table. One is Category and other is sub-category.

In my html form there are a list of select box data which is come from Category table. So i need, if i select this list box, them another select box data will be appear from sub-category table which is related to Category table. For example:

Category table

Id     Cat_name
1      O level  
2      A level.  

Sub-Category table:

id     Cat_id     Sub_name
1      1          O-level Math
2      1          O-level English
3      2          A-level Math
4      2          A-level English

Thanks in Advance.

Answer 1

If you want this to be done seamlessly and efficiently without page reloads you will need to look into the Jquery Ajax function. The way Ajax works is when someone makes a selection in the first box, it will send that data to a php script that can take the answer from the first box, run a mysql query, then return the new subcategories to the original page without having to reload the page.

Example:
In your test.php

//On selection change state, call the ajax
$("#elementid").change(function() {
 var selection = $(this).children("option:selected");

  $.ajax({
    url: 'caller.php',
    dataType: 'json',
    data: 'selected='+selection,
    success: function(data) {
      //Fill the second selection with the returned mysql data
    }
  });
}

<select id="elementid">
  <option value="volvo">Volvo</option>
  <option value="saab">Saab</option>
  <option value="mercedes">Mercedes</option>
  <option value="audi">Audi</option>
</select>

In your caller.php

$selection = $_POST["selected"];
//Create an array to hold all the subcategories, say the array is called $sub
echo json_encode(array(success => $sub));
exit;

Please read up on Jquery.ajax