產品數量組嵌套

Question

見http://mikehillyer.com/articles/managing-hierarchical-data-in-mysql/

在標題「在一組嵌套聚合函數」

我試圖找出給定有類似的例子查詢，除了我想它在子樹級別工作，所以如果我查詢MP3播放器，我會得到一個結果集;

|NAME   |COUNT| 
---------------------- 
|MP3 PLAYERS | 2 | // 2 because 1 at this level and 1 at child level 
|FLASH PLAYERS | 1 | 

Answer 1

假設自參照表tree_node創建如下：

CREATE TABLE tree_node 
(
    id serial NOT NULL, 
    parent integer, 
    "desc" text, 
    l integer, 
    r integer, 
    CONSTRAINT tree_node_pkey PRIMARY KEY (id) 
); 

計數可以用下面的SQL來檢索：

select count(*), p.id, p.desc from tree_node c, tree_node p 
where c.l<=p.r 
and c.l>=p.l 
group by p.id, p.desc;