允许具有嵌套集合结构的多个同名类别

Question

基于 http://mikehillyer.com/articles/managing-hierarchical-data-在-mysql/ 中，我已更改类别层次结构以使用左值和右值。这非常有效，除非两个类别具有相同的名称。

CREATE TABLE `nested_category` (
  `id` mediumint(8) unsigned NOT NULL AUTO_INCREMENT,
  `name` varchar(80) DEFAULT NULL,
  `lft` int(11) NOT NULL DEFAULT '0',
  `rgt` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 AUTO_INCREMENT=28 ;

INSERT INTO `nested_category` VALUES(2, 'Reviews', 3, 20);
INSERT INTO `nested_category` VALUES(6, 'Music2', 24, 25);
INSERT INTO `nested_category` VALUES(18, 'Culture', 2, 21);
INSERT INTO `nested_category` VALUES(19, 'Music', 18, 19);

然后：

SELECT node.name, (
COUNT( parent.name ) -1
) AS depth
FROM nested_category AS node, nested_category AS parent
WHERE node.lft
BETWEEN parent.lft
AND parent.rgt
GROUP BY node.name
ORDER BY node.lft
LIMIT 0 , 30

... 给出：

name  depth 
Culture 0
Reviews 1
Music   2
Music2  0

... 这是完美的。但是，如果我将“music2”更改为“music”，我会得到：

name  depth 
Culture 0
Reviews 1
Music   3

关于如何保持嵌套深度正确，但允许多个类别具有相同名称的任何想法？

Answer 1

将 id 添加到结果和 GROUP BY 以保留您选择的唯一性。

SELECT node.name, id, (
COUNT( parent.name ) -1
) AS depth
FROM nested_category AS node, nested_category AS parent
WHERE node.lft
BETWEEN parent.lft
AND parent.rgt
GROUP BY node.name, id
ORDER BY node.lft
LIMIT 0 , 30