how to write php MySql query - php

Question

I would like to be able to make a selection from a select-box and view the selected table.
My skill level with php/MySQL at this point is:
$query = "SELECT * FROM electrical ORDER BY item_id LIMIT $offset, $RPP";
With this query the div is populated on page load.
I have a select box that has 6 choices:
<form>
<select name="dbtables" onchange="showTable(this.value)" id="selectBox">
<option value="">Select a materials table:</option>
<option value="" id="hr"></option>
<option value="equipment">Worker Equipment</option>
<option value="tool">General Tools</option>
<option value="electrical">Electrical Materials</option>
<option value="mechanical">Mechanical Materials</option>
<option value="plumbing">Plumbing Materials</option>
<option value="hvac">HVAC Materials</option>
</select>
</form>
Each choice is a table in a single MySQL database.
Script for showTable is working, after making selection alert shows choice picked.
function showTable(str) {
if (str == "") {
document.getElementById("materials").innerHTML = "";
return;
}
if (window.XMLHttpRequest) { // code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp = new XMLHttpRequest();
}
else { // code for IE6, IE5
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange = function () {
if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
document.getElementById("materials").innerHTML = xmlhttp.responseText;
}
}
xmlhttp.open("GET", "index.php?q=" + str, true);
xmlhttp.send();
alert(str);
}
Any pointers or help is appreciated appreciated.

Answer 1

I think what you're looking for is the SQL-query to execute on your database. What you should do is to insert the q-variable from the query string into the SQL-query like this
$query = "SELECT * FROM " . $_REQUEST['q'] . " ORDER BY item_id LIMIT $offset, $RPP";
Ofcourse you should check or escape the variables to prevent SQL injections, using something like mysql_real_escape_string, but that's not really the scope of this question.

Answer 2

in your index.php pick the $str value using $_GET method and construct the query. then run that query and echo the data. after that, you can call this function in the script file after alert().
function useHttpResponse() {
if (http.readyState == 4) {
if(http.status == 200) {
var txt = http.responseText;
var response_msg="<h4><span class='darkblue'>" + txt + "</span></h4>"
document.getElementById('showtime').innerHTML = response_msg;
}
} else { //you may skip this else portion
document.getElementById('showtime').innerHTML = '<img src="images/loading.gif" /><span class="darkblue">retrieving data...</span>';
}
}
here your fetched data will show on a div with id "showtime". during the fetching the time a loading gif will be visible in the "showtime" div. or you may skip that else portion.
hope that function will help you.