PHP创建树

Question

我的mysql表看起来像这样：

我需要制作3级树，没有House_NR。

-Country
 |--City 1
 |  |--Street 1
 |  |--Street 2
 |
 |--City 2
 |--City 3
 |  |--Sreet 1
 |  |--Steet 2

在PHP中，我创建了这个SQL查询：

SELECT
    l.Country_ID,
    c1.Name AS Country_Name,
    l.City_ID,
    c2.Name AS City_Name,
    l.Street_ID,
    s.Name AS Street_Name,
    l.House_NR
FROM Location l
JOIN Country c1 ON c1.id = l.Country_ID
JOIN City c2 ON c2.id = l.City_ID
JOIN Street s ON s.id = l.Street_ID

我有这个功能：

function getTree($data) {
    $tree = prepareTree($data);
    drawTree($tree);
}

function prepareTree($data) {
    $nodeList = array();
    $tree = array();

    foreach ($data as $key) {
        $tree[$key["Country_ID"]]["name"] = $key["Country_Name"];
        $tree[$key["Country_ID"]]["id"] = $key["Country_ID"];
        $tree[$key["Country_ID"]]["level"] = 1;

        $tree[$key["Country_ID"]]["children"][$key["City_ID"]]["name"] = $key["City_Name"];
        $tree[$key["Country_ID"]]["children"][$key["City_ID"]]["id"] = $key["City_ID"];
        $tree[$key["Country_ID"]]["children"][$key["City_ID"]]["level"] = 2;

        $tree[$key["Country_ID"]]["children"][$key["City_ID"]]["children"][$key["Street_ID"]]["name"] = $key["Street_Name"];
        $tree[$key["Country_ID"]]["children"][$key["City_ID"]]["children"][$key["Street_ID"]]["id"] = $key["Street_ID"];
        $tree[$key["Country_ID"]]["children"][$key["City_ID"]]["children"][$key["Street_ID"]]["level"] = 3;
    }

    return $tree;
}

function drawTree($data, $sub = false) {
    echo ($sub) ? "<ul class=\"tree-listCat\">" : "<ul class=\"tree-list\">";

    foreach($data as $key) {
        if ($key["children"] != null) {
            echo "<li class=\"tree-itemCat\"><span class=\"tree-itemSel\"><a href=\"switch.php?action=search&type=tree&level=" . $key["level"] . "&id=" . $key["id"] . "\">" . $key["name"] . "</a></span></li>";
            drawTree($key["children"], true);
        } else
            echo "<li class=\"tree-item\"><span class=\"tree-itemSel\"><a href=\"switch.php?action=search&type=tree&level=" . $key["level"] . "&id=" . $key["id"] . "\">" . $key["name"] . "</a></span></li>";
    }

    echo "</ul>";
}

这个函数工作正常，但是函数中有一些问题，函数绘制一个html版本的树现在我有这个：
action=search&type=tree&level=" . $key["level"] . "&id=" . $key["id"]，但我需要这样的东西：

如果只有没有孩子的国家，则为action=search&type=tree&country=id 如果只有国家和城市没有儿童街，那么action=search&type=tree&country=id&city=id
如果所有参数都是country，city和steet，那么action=search&type=tree&country=id&city=id&street_id=id

而且功能准备树看起来很糟糕（在我看来）。简而言之，我需要从Location数据库中创建一个树。