读取树状数据的方法 一般在读取用“邻接列表算法”组织的数据时，需要使用递归逐层读取 或者读取数据到数组，然后用递归或非递归的方法再行处理

tree.php

<?php
mysql_connect();
 
//测试数据
$sql =<<< SQL
select * from (
  select '1' as id, '0' as pid, 'Food' as title
  union all select '2', '1', 'Fruit'
  union all select '3', '2', 'Red'
  union all select '4', '3', 'Cherry'
  union all select '5', '2', 'Yellow'
  union all select '6', '5', 'Banana'
  union all select '7', '1', 'Meat'
  union all select '8', '7', 'Beef'
  union all select '9', '7', 'Pork'
  ) t
  order by pid, id
SQL;
 
$rs = mysql_query($sql);
 
$res = array(); //结果数组
$ind = array(); //索引数组
while($row = mysql_fetch_assoc($rs)) {
  list($id, $pid) = array_values($row); 
  $ind[$id] = $row;
  if(isset($ind[$pid])) $ind[$pid]['child'][$id] =& $ind[$id]; //构造索引
  if($pid == 0) $res[$id] =& $ind[$id]; //转存根节点组
}
 
echo '<xmp>' . print_r($res, 1);

Array
(
[1] => Array
    (
        [id] => 1
        [pid] => 0
        [title] => Food
        [child] => Array
            (
                [2] => Array
                    (
                        [id] => 2
                        [pid] => 1
                        [title] => Fruit
                        [child] => Array
                            (
                                [3] => Array
                                    (
                                        [id] => 3
                                        [pid] => 2
                                        [title] => Red
                                        [child] => Array
                                            (
                                                [4] => Array
                                                    (
                                                        [id] => 4
                                                        [pid] => 3
                                                        [title] => Cherry
                                                    )

                                            )

                                    )

                                [5] => Array
                                    (
                                        [id] => 5
                                        [pid] => 2
                                        [title] => Yellow
                                        [child] => Array
                                            (
                                                [6] => Array
                                                    (
                                                        [id] => 6
                                                        [pid] => 5
                                                        [title] => Banana
                                                    )

                                            )

                                    )

                            )

                    )

                [7] => Array
                    (
                        [id] => 7
                        [pid] => 1
                        [title] => Meat
                        [child] => Array
                            (
                                [8] => Array
                                    (
                                        [id] => 8
                                        [pid] => 7
                                        [title] => Beef
                                    )

                                [9] => Array
                                    (
                                        [id] => 9
                                        [pid] => 7
                                        [title] => Pork
                                    )

                            )

                    )

            )

    )

)