查看
应用程序的视图包含一个页面,该页面显示一组旋转木马(每个旋转木马=一个标签),每个转盘应包含5种产品:
+-------------------------------------+
|Page |
|+-----------------------------------+|
||Tag1 ||
||+--------+ +--------+ +--------+||
|||Product1| |Product2| .. |Product5|||
||+--------+ +--------+ +--------+||
|+-----------------------------------+|
|... |
|+-----------------------------------+|
||TagN ||
||... ||
+-------------------------------------+
数据库
页码
+-------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(16) | NO | UNI | NULL | |
+-------+-------------+------+-----+---------+----------------+
CREATE TABLE `pages` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(16) COLLATE utf8mb4_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
页面\u标签
+--------------+------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+--------------+------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| page_id | int(11) | NO | MUL | NULL | |
| tag_id | int(11) | NO | MUL | NULL | |
| position | tinyint(4) | NO | | NULL | |
+--------------+------------+------+-----+---------+----------------+
CREATE TABLE `pages_tags` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`page_id` int(11) NOT NULL,
`tag_id` int(11) NOT NULL,
`position` tinyint(4) NOT NULL,
PRIMARY KEY (`id`),
KEY `page_id` (`page_id`),
KEY `tag_id` (`tag_id`),
CONSTRAINT `pages_tags_ibfk_1` FOREIGN KEY (`page_id`) REFERENCES `pages` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `pages_tags_ibfk_2` FOREIGN KEY (`tag_id`) REFERENCES `tags` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=663 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
标签
+---------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(128) | NO | | NULL | |
+---------+--------------+------+-----+---------+----------------+
CREATE TABLE `tags` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(128) COLLATE utf8mb4_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
) ENGINE=InnoDB AUTO_INCREMENT=149 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
产品标签
+------------+---------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+------------+---------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| product_id | int(11) | NO | MUL | NULL | |
| tag_id | int(11) | NO | MUL | NULL | |
+------------+---------+------+-----+---------+----------------+
CREATE TABLE `products_tags` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`product_id` int(11) NOT NULL,
`tag_id` int(11) NOT NULL,
PRIMARY KEY (`id`),
KEY `tag_id` (`tag_id`),
KEY `bouquet_id` (`product_id`),
CONSTRAINT `products_tags_ibfk_1` FOREIGN KEY (`product_id`) REFERENCES `products` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
CONSTRAINT `products_tags_ibfk_2` FOREIGN KEY (`tag_id`) REFERENCES `tags` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB AUTO_INCREMENT=5698 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
产品
+-------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
| name | varchar(128) | NO | UNI | NULL | |
+-------------+--------------+------+-----+---------+----------------+
CREATE TABLE `products` (
`id` int(11) NOT NULL AUTO_INCREMENT,
`name` varchar(128) COLLATE utf8mb4_unicode_ci NOT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `name` (`name`)
) ENGINE=InnoDB AUTO_INCREMENT=335 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci
目标
目标是得到一个输出,其中包含页面上的所有标签,每个标签最多包含5个产品。
查询
以下是我遇到的问题:
SELECT t.name, p.name
FROM pages a
LEFT JOIN pages_tags a_t ON a_t.page_id = a.id
LEFT JOIN tags t ON t.id = a_t.tag_id
LEFT JOIN products p ON p.id = (
SELECT p_t.product_id FROM products_tags p_t WHERE p_t.tag_id = t.id LIMIT 1
);`
问题
无法使用 limit 5
:
错误1242(21000):子查询返回超过1行
无法使用 in
+ limit
:
错误1235(42000):此版本的mysql尚不支持“limit&in/all/any/some子查询”
需要帮助。
我要返回的内容(示例)
页码
标签1
产品1
产品2
产品3
产品4
产品5
标签2
产品6
产品7
产品8
产品9
产品10
...
塔根
产品K
productl(但总是最大值为5)
1条答案
按热度按时间gcmastyq1#
您可以使用标量子查询执行所需的操作:
但是,如果行数少于5行,则此操作不起作用。在这种情况下,你可以使用
coalesce()
:注意:这假设您希望产品标识按顺序排列。