[英]MySQL many-to-many SELECT query
I have a Product table, a Tags table and a table that links them together, ProductTags . 我有一个产品表,一个标签表和一个将它们链接在一起的表ProductTags 。
Product 产品
ID
ProductTags ProductTags
ProductID
TagID
Tags 标签
ID
I want to query the ProductTags
table for all ProductIDs
that have both TagID
1 and 2. How would I do this? 我想在
ProductTags
表中查询同时具有TagID
1和2的所有ProductIDs
。我该怎么做?
SELECT *
From ProductTags
Where TagID = 1
AND TagID = 2
This obviously won't work... can't quite get my head round how to do it! 这显然行不通...无法完全理解该怎么做!
Any help much appreciated! 任何帮助,不胜感激!
This is a "set-within-sets" query and I like to solve these using group by
and having
. 这是一个“组内查询”查询,我喜欢使用
group by
和having
来解决这些问题。 Here is one method: 这是一种方法:
SELECT ProductId
FROM ProductTags
WHERE TagID IN (1, 2)
GROUP BY ProductId
HAVING COUNT(DISTINCT TagId) = 2;
You need to use group by and having for this case 您需要在这种情况下使用分组依据
select
p.id
from product p
join producttags pt on pt.ProductID = p.id
join tags t on t.id = pt.tagid
where pt.tagid in (1,2)
group by p.id
having count(*) = 2
尝试两次加入ProductTags
表。
SELECT t3 From ProductTags t1 join ProductTags t2 on t1.productId=t2.productId join Product t3 Where t1.TagID = 1 AND t2.TagID = 2
Try This: 尝试这个:
SELECT * From ProductTags
Where TagID = 1 OR TagID = 2
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