作为我第一个回答的后续，下面的示例展示了如何使用单个查询来完成此操作.恕我直言，您应该始终选择这种方法.如果您只有少数几个类别要钻取，如果您坚持使用查询嵌套在循环内的方法，则性能消耗可能不会太大.但如果您有大量类别，下面的方法应该会更有效:

As a follow-up to my first answer, the example below shows how you can do this with a single query. IMHO, you should always opt for this approach. If you only have a handful of categories to drill into, it may not be much of a performance drain if you stick with the query-nested-inside-a-loop approach. But if you have a sizable number of categories, the approach below should be significantly more efficient:

require 'db/connect.php';
$sql = "
    SELECT
        category.id
        , links.links
    FROM
        category
    LEFT JOIN
        links ON links.catID = category.id
    ORDER BY
        category.id ASC
        -- this ORDER BY is critical, it ensures that all of the
        -- records will be lumped by category
";
// (yes, this query will create multiple rows for every category, but that's OK,
// we're going to deal with that in the while() loop
$results = $db->query($sql);
echo "<p class='post-footer align-left'><span class='pageName'><span class='style3'>Links</span></span></p>";
if($results->num_rows){
    $previousId = '';
    while($row = $results->fetch_object()){
        $currentId = $row->id;
        if ($currentId !== $previousId) {
            // we only show the wrapper <table>, and the category header, if we've encountered a new
            // batch of rows which signifies that a new category is being processed
            echo "<table width='507' border='1'>";
            echo " <p class='post-footer align-left'><span class='pageName'><span class='style3'>{$row->cat}</span></span></p>";
        }
        echo "<th><span class='pageName'><span class='style3'>{$row->links}</span></span></th>";
        if ($currentId !== $previousId and $previousId !== '') {
            echo "</table>";  // this wasn't in your original code, but I assume it should be here
        }
        $previousId = $currentId;
    }
}
echo "</table>";