我有两个表:类别和项目。我使用嵌套集结构存储类别。类别有项目。项目只能添加到根类别的叶节点。
例如: 类别
Vehicles
Bikes
Bajaj
Automobiles
Art & Antiques
Amateur Art
在这种情况下,可以将项目添加到类别 Bajaj、汽车和业余艺术。
假设 Bajaj 中有 2 个项目,Automobiles 中有 5 个项目,Amateur Art 中有 2 个
对于根级别类别,我想显示如下:
- Vehicles (7 items)
- Art & Antiques (2 items)
我该怎么做?
这是处理一些示例数据的 sql 转储
--
-- Table structure for table `categories`
--
CREATE TABLE IF NOT EXISTS `categories` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`parent_id` int(11) DEFAULT NULL,
`title` varchar(64) COLLATE utf8_unicode_ci NOT NULL,
`lft` int(11) NOT NULL,
`lvl` int(11) NOT NULL,
`rgt` int(11) NOT NULL,
`root` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
KEY `IDX_3AF34668727ACA70` (`parent_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci AUTO_INCREMENT=28 ;
--
-- Dumping data for table `categories`
--
INSERT INTO `categories` (`id`, `parent_id`, `title`, `lft`, `lvl`, `rgt`, `root`) VALUES
(22, NULL, 'Vehicles', 1, 0, 8, 22),
(23, 22, 'Bikes', 2, 1, 5, 22),
(24, 23, 'Bajaj', 3, 2, 4, 22),
(25, 22, 'Automobiles', 6, 1, 7, 22),
(26, NULL, 'Art & Antiques', 1, 0, 4, 26),
(27, 26, 'Amateur Art', 2, 1, 3, 26);
-- --------------------------------------------------------
--
-- Table structure for table `items`
--
CREATE TABLE IF NOT EXISTS `items` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`category_id` int(11) NOT NULL,
`title` varchar(100) NOT NULL,
PRIMARY KEY (`id`),
KEY `FK_403EA91BA33E2D84` (`category_id`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1 AUTO_INCREMENT=5 ;
--
-- Dumping data for table `items`
--
INSERT INTO `items` (`id`, `category_id`, `title`) VALUES
(1, 24, 'Pulsor 150 cc'),
(2, 24, 'Discover 125 cc'),
(3, 27, 'Art of dream'),
(4, 25, 'Toyota Car');
--
-- Constraints for dumped tables
--
--
-- Constraints for table `categories`
--
ALTER TABLE `categories`
ADD CONSTRAINT `FK_3AF34668727ACA70` FOREIGN KEY (`parent_id`) REFERENCES `categories` (`id`) ON DELETE SET NULL;
--
-- Constraints for table `items`
--
ALTER TABLE `items`
ADD CONSTRAINT `FK_403EA91BA33E2D84` FOREIGN KEY (`category_id`) REFERENCES `categories` (`id`) ON DELETE CASCADE;
根节点的parent_id字段为NULL
更新:
我能够使用此查询获取根:
SELECT c.id,c.title,cte.co FROM categories c
JOIN
(SELECT
c0_.id,c0_.root,COUNT(i.id) co
FROM
categories c0_
JOIN items i ON c0_.id=i.category_id
WHERE c0_.rgt = 1 + c0_.lft
GROUP BY c0_.id
) cte
ON cte.root=c.id
WHERE c.parent_id is null
以上查询适用于根级别类别。现在,当用户点击根级别类别时,我也想这样做。
例如,当有人点击车辆时,我应该得到:
Bikes (2)
Automobiles (5)
为此我尝试了:
SELECT c.id,c.title,cte.co FROM categories c
JOIN
(SELECT
c0_.id,c0_.root,COUNT(i.id) co
FROM
categories c0_
JOIN items i ON c0_.id=i.category_id
WHERE
c0_.rgt = 1 + c0_.lft
GROUP BY c0_.id
) cte
ON cte.root=c.id
WHERE c.parent_id=1
这返回了空结果集。这个查询有什么问题?
最佳答案
SELECT parent.title,
( SELECT count(i.id) count FROM items i
WHERE category_id IN
(
SELECT child.id FROM categories child WHERE child.lft>=parent.lft AND
child.rgt<=parent.rgt AND child.root=parent.root
)
)
FROM categories parent
WHERE parent.parent_id=@parent_id;
如果不行请通知我
关于mysql - 在sql中获取与嵌套类别相关的项目数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/15457030/