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    <p>You should combine your <code>top_category</code> and <code>bottom_category</code> tables into a single table, perhaps <code>category</code>. There's really no reason that these need to be separated. It would look like this:</p> <pre><code>CREATE TABLE category ( id INT PRIMARY KEY, parent_id INT, NAME VARCHAR(100) ); </code></pre> <p>For all "top" categories, the <code>parent_id</code> would be 0. For any "bottom" categories, the <code>parent_id</code> would be the <code>id</code> of the "top" category under which it falls. In addition to cleaning up the database a bit, it allows for future expansion into more than just two layers if you desired.</p> <p>Then you'd create a recursive function (a function that calls itself) to loop through and display the menu structure, something like this:</p> <pre><code>function menus( $parent_id, $pdo ) { $menu_query = "SELECT * FROM category WHERE parent_id = :parent_id"; $menu_result = $pdo-&gt;prepare( $menu_query ); $menu_result-&gt;execute( array( ":parent_id" =&gt; $parent_id )); $menu = ""; if( $menu_result-&gt;rowCount() ) { $menu .= "&lt;ul&gt;\n"; while( $menu_row = $menu_result-&gt;fetch( PDO::FETCH_ASSOC )) { $menu .= "&lt;li&gt;{$menu_row['NAME']}\n"; $menu .= menus( $menu_row['id'], $pdo ); $menu .= "&lt;/li&gt;\n"; } $menu .= "&lt;/ul&gt;\n"; } return $menu; } </code></pre> <p>Then to display your menu, you'd simply print the results of the function:</p> <pre><code>print menus( 0, $pdo ); </code></pre> <p>It'll return a structure that basically looks like this:</p> <pre><code>&lt;ul&gt; &lt;li&gt;prod1 &lt;ul&gt; &lt;li&gt;subprod1&lt;/li&gt; &lt;li&gt;subprod2&lt;/li&gt; &lt;li&gt;subprod3&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;li&gt;prod2 &lt;ul&gt; &lt;li&gt;subprod4&lt;/li&gt; &lt;li&gt;subprod5&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;li&gt;prod3 &lt;ul&gt; &lt;li&gt;subprod6&lt;/li&gt; &lt;/ul&gt; &lt;/li&gt; &lt;/ul&gt; </code></pre> <p>(Indentation added for readability, the code above does not add the indentation, but that's the structure).</p> <p>Here's essentially what this does. The function pulls all of the top-level entries, then as it loops through each one, it calls itself but with the ID of the currently-selected entry, which then pulls all of the children, and does the same thing. Each time it completes a layer (i.e. creates the structure for all entries at a given level), it returns that to the parent function and concatenates the data.</p> <p>I haven't tested this specific code, so it may contain a minor issue here or there, but the concept is solid (I've implemented it many times myself).</p> <p><strong>UPDATE (styling)</strong></p> <p>If you want to apply styles to this menu where each layer has a different set of styles, there are two ways to do this. The first is to a $level variable to the function so that it'd be defined like this:</p> <pre><code>function menus( $parent_id, $pdo, $level ) </code></pre> <p>Start out by calling it with <code>0</code> for the level, then within the function call it with <code>$level + 1</code>. This way, each successive level will be called with the correct value. You can create classes based on this, such as <code>level-1</code>, then define the element as having <code>class="level-{$level}"</code>.</p> <p>The second is to wrap the entire thing in a <code>&lt;div&gt;</code>, and then use immediate child selectors to reference a specific level. <code>div&gt;ul&gt;li</code> would be the first level of <code>&lt;li&gt;</code>, <code>div&gt;ul&gt;li&gt;ul&gt;li</code> would be the second level of <code>&lt;li&gt;</code>, and so on.</p>
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    1. COOkay i will give it a try thanks.
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    2. COI am getting a few errors, Undefined variable: pdo, and Fatal error: Call to a member function prepare() on a non-object in... sidebar.php and missing argument 2 for menus()... i had more errors but i fixed them. these ones i am unable to work out.
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    3. CO`$pdo` represents your PDO object for your DB connection. Change it to whatever you're using. The error `Fatal error: Call to a member function prepare()` will be fixed bu this as well. I edited the code to fix `missing argument 2 for menus()`.
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