Selecting rows that are included in a set from another table - mysql

Question

I have a table "Products" with a product name and id:
id | title
1 product 1
2 product 2
Each product can have a series of tags. Tags are identified in table "Attributes":
id | name | handle
1 Tag One tag-one
2 Tag Two tag-two
3 Tag Three tag-three
4 Tag Four tag-four
etc
The product to tag relationship is another table "Tags":
id | AttId | OwnerId
1 1 1
2 2 1
3 1 2
4 3 2
etc
Ok, so I am trying to select a set of products that all have at least one specific tag, and a possible selection of other tags. Here is what I am working with now:
SELECT products.id
FROM products
WHERE
EXISTS
(
SELECT 1
FROM Tags
INNER JOIN Attributes ON tags.AttId = Attributes.id
WHERE Attributes.handle = 'tag-one'
AND (
Attributes.handle = 'tag-two'
OR
Attributes.handle = 'tag-four'
)
AND products.id = Tags.OwnerId
)
If I remove the AND (OR) section, the query works. As above, it shows no errors, but also no results; How should I write this so I can get a set of products that have one tag for sure, AND have either/or other specified tags by the tag handle?

Answer 1

I like to approach this type of problem using group by and having -- because I find that this method works very well for expressing many different conditions. For your conditions:
select p.*
from products p join
tags t
on t.OwnerId = p.id join
attributes a
on t.attid = a.id
group by p.id
having sum(a.handle = 'tag-one') > 0 and
sum(a.handle in ('tag-two', 'tag-four')) > 0;
Each condition in the having clause counts the number of rows (for a product) that match a condition. The first says there is at least one row with 'tag-one' handle. The second says that there is at least one row with the other two handles.

Answer 2

I think if you perform two separate queries and take the intersection, that will give you what you want.
-- Get all the owner ids that have 'tag-one'
select OwnerId
from Tags t1
where AttId in
(
select id
from Attributes a1
where a1.handle = 'tag-one'
)
intersect
-- Get all the owner ids that have tag-two and tag-four
select OwnerId
from Tags t2
where AttId in
(
select id
from Attributes a2
where a2.handle in ('tag-two', 'tag-four')
)
;