PHP Drop Down Selected - php

Question

i've got 3 drop down boxes which populate each drop down from the one above but on the 3rd drop down i want it to bring back a value that i selected. The code is below
<tr>
<td width="119">Category</td>
<td width="371">
<select name="cat_id" id="cat_id" onChange="showCompany(this.value);">
<option value="">--Select--</option>
<?php
$sql="select * from category";
$sql_row=mysql_query($sql);
while($sql_res=mysql_fetch_assoc($sql_row))
{
?>
<option value="<?php echo $sql_res["id"]; ?>" <?php if($sql_res["id"] ==$_REQUEST ["cat_id"]) { echo "Selected"; } ?>><?php echo $sql_res["category_name"]; ? ></option>
<?php
}
?>
</select>
</td>
</tr>
<tr>
<td>Company</td>
<td id="td_company">
<select name="company_id" id="company_id">;
<option value="">--Select--</option>
<?php
$sql="select * from company where cat_id='$_REQUEST[cat_id]'";
$sql_row=mysql_query($sql);
while($sql_res=mysql_fetch_assoc($sql_row))
{
?>
<option value="<?php echo $sql_res["id"]; ?>"><?php echo $sql_res["company_name"]; ?></option>
<?php
}
?>
</select>
</td>
</tr>
<tr>
<td>Item</td>
<td id="td_item">
<select name="item_id" id="item_id">
<option value="">--Select--</option>
<?php
$sql="select * from item where comp_id='$_REQUEST[cat_id]'";
$sql_row=mysql_query($sql);
while($sql_res=mysql_fetch_assoc($sql_row))
{
?>
<option value="<?php echo $sql_res["id"]; ?>"><?php echo $sql_res["item_name"]; ?></option>
<?php
}
?>
</select>
</td>
</tr>
<tr>
<td>Price</td>
<td id="td_item">
<?php
$sql="select unit_cost from item where comp_id='$_REQUEST[cat_id]'";
$sql_row=mysql_query($sql);
while($sql_res=mysql_fetch_assoc($sql_row))
{
echo "<td>" . "&pound" . $sql_res['unit_cost'] . "</td>";
}
?>
</td>
</tr>
<tr>
</tr>
</table>
</form>
so basically i want it to bring back the price from the option i selected, at the moment its bringing back all prices.
e.g. first drop down i select cellings then the company drop down i select Access Panels then 3rd drop down they is 3 items (Arm Strong, Track and Screw) and it brings back all 3 prices where i want to be able to select one and only bring back that price. any ideas?

Answer 1

First off you shouldn't be using mysql_* functions, they're deprecated. Look into either mysqli or PDO. Second, you have a vulnerability in your code where you are inserting $_REQUEST straight into your SQL. That's called SQL Injection. You should probably do some reading on it.
With all that in mind the problem is your query is trying to select all of the items where company id = category id. This is your query:
$sql="select * from item where comp_id='$_REQUEST[cat_id]'";
Notice the comp_id='$_REQUEST[cat_id]' should it instead be something like comp_id = $_REQUEST[comp_id]'?