Query MySQL results using PHP and multiple HTML dropdown boxes from multiple tables including 'id' reference tables

Tables structure:

TESTLINKS

• id
• source
• projectid
• clientid
• qa
• stg
• prod
• username
• password

PROJECTS

• id
• projectname
• clientid
• projectdescription
• projectmanager
• qbid
• aetid
• uatdate
• targetreleasedate
• status

PRODUCTS

• id
• productname
• projectmanageruserid

TESTLINKSPRODUCTS

• id
• testlinksid
• productsid

CLIENTS

• id
• clientname
• clientmanager

My goal is to create a system to input testing links and to enable the user to pull the appropriate testing links based on multiple options which they can select in a series of dropdown boxes.

I have setup the PHP and HTML pages to input data into the tables listed above. Now I am trying to setup the MySQL query and PHP required to pull the data into the webpage.

I would like the user to be able to query the results based on 1) projects.id 2) testlinks.source 3) products.id 4) clients.id

these would be selected from 4 separate dropdown boxes

I was easily able to successfully pull results based on projects.id and testlinks.source because these two tables have 'projectid' in common. However I am now having an issue pulling results based on 'productid' because the products are associated to the testlinks and not to the projects. The 'testlinksproducts' table handles the association of products to testlinks but I do not know how to add this to the query because when I run the query I get rows repeated several times and doesn't achieve the results that I want.

Here is my PHP file which is working for pulling testlinks based on project.id and testlinks.source --

$query = "SELECT testlinks.id,
                 testlinks.source,
                 testlinks.projectid,
                 testlinks.clientid,
                 testlinks.qa,
                 testlinks.stg, 
                 testlinks.prod, 
                 testlinks.username,
                 testlinks.password, 
                 projects.id, 
                 projects.projectname 
          FROM testlinks , projects 
          WHERE testlinks.projectid = projects.id 
            AND (testlinks.projectid='$projectid' 
                 OR testlinks.source='$source')
          ;"; 

$result = mysql_query($query) or die(mysql_error()); 

echo "<table class=\"zebra\">"; 
echo "<thead><tr>
    <th>ID</th>
    <th>Source</th>
    <th>Project Name</th>
    <th>QA</th>
    <th>STG</th>
    <th>Prod</th>
    </tr></thead>";
while($row = mysql_fetch_array($result))
{
    echo "<tr>"; 
    echo "<td>".$row['id']."</td>
        <td>".$row['source']."</td>
        <td>".$row['projectname']."  </td>
        <td>"."<a href=\"".$row['qa']."\" target=\"new\">
            <button>QA</button></a></td>
        <td>"."<a href=\"".$row['stg']."\" target=\"new\">
            <button>STG</button></a></td>
        <td>"." <a href=\"".$row['prod']."\" target=\"new\">
            <button>PROD</button></a></td>
        </tr>";
}
echo "</table>";

Can someone help with adding query functionality to pull testlinks based on productsid (contained in 'testlinksproducts' table) ?

Help would be very much appreciated on this one!

Thanks