下面是我的数据库结构(MySql)：

类别

+-------------+------------+
 category_id  | parent_id  |
+-------------+------------+
  1           |      0     
  2           |      1
  3           |      1
  4           |      1
  5           |      2
  6           |      3

PRoducts_to_categories

+-------------+------------+
 product_id   | category_id|
+-------------+------------+
  54          |      0     
  55          |      2
  56          |      2
  57          |      2
  58          |      3
  59          |      3
  60          |      4

制品

+-------------+------------+
 product_id   |    price   |
+-------------+------------+
  54          |      10.50     
  55          |      11.20
  56          |      1.00
  57          |      22.20
  58          |      32.0
  59          |      32.0
  60          |      22.0

以下是我的情况;

1. table categories : parent_id = '1'  
(result : 2,3,4)

2. table products_to_categories : category_id = result categories(result : 2,4) 
(result : 55,56,57,58,59,60)

3. table products : inner join or left join table product to display price where product_id = result products_to_categories(result : 55,60)

最终产出

55 - 11.20
  56 - 1.00
  57 - 22.20
  58 - 32.0
  59 - 32.0
  60 - 22.0

在我发布这个问题之前,这是我之前的查询(我坚持如何进入条件2)

$sql_all = MysqL_query("SELECT cat.parent_id,cat.category_id From categories cat WHERE cat.parent_id='1' ");
while($row = MysqL_fetch_array($sql_all)) {
echo $row['categories_id'].'<br/>'; 
}

谢谢.