Displaying category list on sidebar of web page

PHP newbie here. I'm currently developi开发者_开发技巧ng a shopping cart web site using PHP and my question is how do I make a dynamic category tree listing on my side bar? Because I have no idea on how to implement it. I'm done with adding of categories in database.

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With the limited information you provided on how many levels of categories you require, here is an example that may help?

    // create a function to get the categories
    function getCategories() {
        // query the top level categories
        $query = "SELECT catId,catName FROM categories ORDER BY catName";
        $result = mysql_query($query);
        // check that you got some results before proceeding
        if (mysql_num_rows($result)>0) {
            // create a $html variable to return from the function
            $html = '<ul class="L1-categories">';
            // loop through the results
            while ($rows = mysql_fetch_object($result)) {
                // append top level cats to your $html variable
                $html .= '<li><a href="index.php?category='.$rows->catId.'">'.$rows->catName.'</a>';
                // repeat the above query for 2nd level categories (sub cats)
                $queryL2 = "SELECT subId,subName FROM subCategories WHERE catId=".$rows->catId." ORDER BY subName";
                $resultL2 = mysql_query($queryL2);
                // check you got results
                if (mysql_num_rows($resultL2)>0) {
                    // continue appending the variable with some html that show sub cats indented
                    $html .= '<ul class="L2-categories">';
                    // loop through the sub cats
                    while ($rowsL2 = mysql_fetch_object($resultL2)) {
                        // if there were sub sub cats etc you just keep this code going deeper
                        $html .= '<li><a href="index.php?category='.$rows->catId.'&sub='.$rowsL2->subId.'">'.$rowsL2->subName.'</a></li>';
                    } // end sub cats loop
                    $html .= '</ul>';
                } // end check for results
                $html .= '</li>';
            } // end top level cats loop
            $html .= '</ul>';
        }
        return $html;
    }

    // usage
    echo getCategories();

Style up your L1-categories and L2-categories in your css file as required for your side bar and you should be on your way, those links will need to change to suit your website they are just there for an example