Question

I have a problem with mysql query, it’s complex problem which relates to Mysql join query for multiple "tags" (many-to-many relationship) that matches ALL tags?

So I have classic MN table schema:

Item
1 | Item1
2 | Item2
...

Category
1 | Category1
2 | Category2
3 | Category3
4 | Category4
...

Item_has_category
1 | 1
...

And question is – How can I get rows, where item has Category1 OR Category2 AND Category3?

It is for some complex filter and some categories has a special group, which must be with AND.

I suppose that I must combine HAVING with DISTINCT (link to another questions at top), but I’m not sure how.

Answer 1

This group by would work:

select  ItemId
from    Item_has_category
group by
        ItemId
having  sum(case when CategoryId = 1 then 1 end) = 1
        or sum(case when CategoryId = 2 then 1 end) = 1
        andsum(case when CategoryId = 3 then 1 end) = 1