php - 列出父子树结构

Question

我有多层父子关系，我想以树结构列出它们。我有一个包含 id、parent_id 等字段的表。我尝试过

$sql    = 'SELECT * FROM list WHERE parent_id = 0';
$result = mysql_query($sql, $link);
while ($row = mysql_fetch_array($result)) {
    echo $row['id'].'<br>';
    $child1_sql = "SELECT * FROM list WHERE parent_id = ".$row['id'];
    $result1 = mysql_query($child1_sql, $link);
    while ($row1 = mysql_fetch_array($result1)) {
        $id = my_recursive_function($row1['parent_id'],$link);
        echo $id;
    }
}   

function my_recursive_function($parent_id,$link) {

    $child2_sql = "SELECT * FROM list WHERE parent_id = ".$parent_id;
    $result2 = mysql_query($child2_sql, $link);
    $row_cnt = mysql_num_rows($result2);

    if($row_cnt > 0) {
        while ($row = mysql_fetch_array($result2)) {
            if($row['parent_id'] == 0) {
                return $row['id'];
            } else {
                my_recursive_function($row['parent_id'],$link);
            }
        }
    }
}

但它给了我

Fatal error:  Out of memory (allocated 126877696) (tried to allocate 24 bytes)

Answer 1

你应该优化sql查询，而不是使用php递归。有一篇关于此的好文章，也许可以帮助您:

http://web.archive.org/web/20110606032941/http://dev.mysql.com/tech-resources/articles/hierarchical-data.html