mysql内部连接条件忽略重复的ID

Posted 2023-02-24

【中文标题】mysql内部连接条件忽略重复的ID

【英文标题】：mysql inner join condition to ignore duplicate ids

【发布时间】：2013-02-27 05:01:03

【问题描述】：

在表格列表下方给出。

根据位置 [23,24,25,26,27] 中产品的点击次数总和，按降序排列商店 ID。

给定 product_id = 8

---

link_shops_locations

shop_id | location_id
---------------------
1       | 23
2       | 24
3       | 25
3       | 26
3       | 27

---

products_clicks

shop_id | product_id | clicks
-----------------------------
1       | 8          | 1
2       | 7          | 3
2       | 8          | 87
3       | 8          | 21
3       | 8          | 9

---

link_products_shops

product_id | shop_id
---------------------
 7         | 1
 8         | 1
 8         | 1
 8         | 2
 8         | 2
 8         | 1
 7         | 3
 8         | 3

这是我尝试过的，

SELECT SUM(c.clicks) as no,
       s.shop_id
FROM  link_products_shops l
INNER JOIN products_clicks c
ON c.product_id = l.product_id
INNER JOIN link_shops_locations s
ON s.shop_id = c.shop_id // duplicate shop_ids gives wrong SUM
WHERE s.location_id IN (23,24,25,26,27)
GROUP BY s.shop_id
ORDER BY no DESC;

我的问题是，由于link_shops_locations表有3个shop_id，所以得到的期望SUM乘以3。我该如何解决？ link_shops_locations的INNER JOIN条件与此有关吗？ .一点帮助将非常有用。

【参考方案1】：

[1]您在 INNER JOIN with products_clicks 中又错过了一个条件。

[2]你也忽略了product_id。看看这个查询。

[3]您在link_products_shops 表中插入了三次product_id=8 and shop_id=1。

    select shop_id, SUM(NoOfClicks) FROM(SELECT distinct c.shop_id, c.clicks AS NoOfClicks 
FROM  products_clicks c 
INNER JOIN link_products_shops l 
ON c.product_id = l.product_id 
AND c.shop_id = l.shop_id 
INNER JOIN link_shops_locations s 
ON s.shop_id = c.shop_id and s.shop_id = l.shop_id 
WHERE s.location_id IN (23,24,25,26,27) 
AND c.product_id = 8) AS TabShopCounters
GROUP BY shop_id
ORDER BY NoOfClicks DESC;

SQL 小提琴 - http://www.sqlfiddle.com/#!2/b22fe/8

【讨论】：

好吧，我错过了。我现在明白了。但是，我的问题仍然是对于 lcoations 25、26、27 会有重复的 shop_ids，即 3。因此，生成的 SUM(clicks) 乘以 3。如何使其唯一？。

为什么link_products_shops 中有重复的行。删除它们并检查。用小提琴更新了我的查询和答案