在另一个while循环中使用while循环的结果

作为我的第一个答案的后续操作，以下示例显示了如何使用单个查询即可完成此操作。恕我直言，您应该始终选择这种方法。如果您只有少数几类可以钻取，那么坚持使用“查询嵌套内部循环”方法可能不会浪费很多性能。但是，如果您有相当多的类别，则下面的方法应该会大大提高效率：

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>";