如何使用多对多关系优化mysql COUNT()查询(通过第三个表)
以下是我执行的查询:如何使用多对多关系优化mysql COUNT()查询(通过第三个表),mysql,sql,group-by,count,many-to-many,Mysql,Sql,Group By,Count,Many To Many,以下是我执行的查询: SELECT COUNT(*) FROM (SELECT `p`.* FROM `shop_products` `p` LEFT JOIN `shop_tag_assignments` ON `p`.`id` = `shop_tag_assignments`.`product_id` LEFT JOIN `shop_tags` ON `shop_tag_assignments
SELECT COUNT(*)
FROM (SELECT `p`.*
FROM `shop_products` `p` LEFT JOIN
`shop_tag_assignments`
ON `p`.`id` = `shop_tag_assignments`.`product_id` LEFT JOIN
`shop_tags`
ON `shop_tag_assignments`.`tag_id` = `shop_tags`.`id`
WHERE `p`.`status`=1
GROUP BY `p`.`id`
) `c`
这个查询大约需要300毫秒(我觉得太长了…)
解释问题:
数据库表转储:
车间标签中的1k记录
CREATE TABLE `shop_tags` (
`id` int(11) NOT NULL,
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`slug` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`label` text COLLATE utf8_unicode_ci NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
ALTER TABLE `shop_tags`
ADD PRIMARY KEY (`id`),
ADD UNIQUE KEY `idx-shop_tags-slug` (`slug`),
ADD KEY `id` (`id`);
ALTER TABLE `shop_tags`
MODIFY `id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=1162;
COMMIT;
CREATE TABLE `shop_tag_assignments` (
`product_id` int(11) NOT NULL,
`tag_id` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE `shop_tag_assignments`
ADD PRIMARY KEY (`product_id`,`tag_id`),
ADD KEY `idx-shop_tag_assignments-product_id` (`product_id`),
ADD KEY `idx-shop_tag_assignments-tag_id` (`tag_id`),
ADD KEY `_index_name` (`product_id`,`tag_id`),
ADD KEY `__index_name` (`tag_id`,`product_id`);
ALTER TABLE `shop_tag_assignments`
ADD CONSTRAINT `fk-shop_tag_assignments-product_id` FOREIGN KEY (`product_id`) REFERENCES `shop_products` (`id`) ON DELETE CASCADE,
ADD CONSTRAINT `fk-shop_tag_assignments-tag_id` FOREIGN KEY (`tag_id`) REFERENCES `shop_tags` (`id`) ON DELETE CASCADE;
COMMIT;
车间标签分配的表结构:
车间标签作业中的224k条记录
CREATE TABLE `shop_tags` (
`id` int(11) NOT NULL,
`name` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`slug` varchar(255) COLLATE utf8_unicode_ci NOT NULL,
`label` text COLLATE utf8_unicode_ci NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;
ALTER TABLE `shop_tags`
ADD PRIMARY KEY (`id`),
ADD UNIQUE KEY `idx-shop_tags-slug` (`slug`),
ADD KEY `id` (`id`);
ALTER TABLE `shop_tags`
MODIFY `id` int(11) NOT NULL AUTO_INCREMENT, AUTO_INCREMENT=1162;
COMMIT;
CREATE TABLE `shop_tag_assignments` (
`product_id` int(11) NOT NULL,
`tag_id` int(11) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
ALTER TABLE `shop_tag_assignments`
ADD PRIMARY KEY (`product_id`,`tag_id`),
ADD KEY `idx-shop_tag_assignments-product_id` (`product_id`),
ADD KEY `idx-shop_tag_assignments-tag_id` (`tag_id`),
ADD KEY `_index_name` (`product_id`,`tag_id`),
ADD KEY `__index_name` (`tag_id`,`product_id`);
ALTER TABLE `shop_tag_assignments`
ADD CONSTRAINT `fk-shop_tag_assignments-product_id` FOREIGN KEY (`product_id`) REFERENCES `shop_products` (`id`) ON DELETE CASCADE,
ADD CONSTRAINT `fk-shop_tag_assignments-tag_id` FOREIGN KEY (`tag_id`) REFERENCES `shop_tags` (`id`) ON DELETE CASCADE;
COMMIT;
Mysql版本:
5.7.16-10-log删除子查询。而且不要经常使用反勾号:
SELECT COUNT(DISTINCT p.id)
FROM shop_products p LEFT JOIN
shop_tag_assignments sta
ON p.id = sta.product_id LEFT JOIN
shop_tags st
ON sta.tag_id = st.id
WHERE p.status = 1;
对于此查询,您需要有关shop\u产品(状态,id)
的索引
接下来,您的查询将计算内部子查询通过p.id
聚合后返回的行数。您使用的是左联接
,因此未筛选出任何内容。这意味着连接实际上是冗余的。我认为这也是同样的道理:
SELECT COUNT(*)
FROM shop_products p
WHERE p.status = 1;
这应该比你的版本快得多。但是,您的版本非常快,因此您可能不会注意到有太大的差异。此查询中需要“LEFT JOIN”,因为我想按产品的标记名筛选产品。很抱歉没有事先澄清这一点。也许还有另一种方法可以计算产品的数量,并分别按标签名称进行过滤?这不是这个问题所问的问题,但您可以在第一次查询中使用
where
。