Find items with maximum matching attributes - mysql

Question

Here is my table structure - table name "propAssign"
(indexed) (composite index for attributeName and attributeValue)
productId attributeName attributeValue
1 Height 3
1 Weight 1
1 Class X1
1 Category C1
2 Height 2
2 Weight 2
2 Class X2
2 Category C1
3 Height 3
3 Weight 1
3 Class X1
3 Category C1
4 Height 4
4 Weight 5
4 Class X2
4 Category C3
What I want to do is, get list of productId, sorted by maximum matching attributes-value pair. In real table, I am using numeric ID of attribute name and value, I've used text here for easy representation.
So if I want to find matching products of productId=1, I want it to look for product which has maximum match (like Height=3, Weight=1, Class=X1 and Category=C1). There may not be any with 100% match (all 4 match) but if there are, they should come first, next comes productId which has any 3 attributes matching, then any 2, etc.
I could add more indexes if required, better if I don't have to since there are millions rows. It's MariaDB v10 to be exact.
Desired result - If I try to find matching product for productId=1, it should return following, in same order.
productId
-----------
3
2
Reason - 3 has all attributes matching with 1, 2 has some matches and 4 has no match.

Answer 1

You can use conditional aggregation to retrieve the productId's with the highest number of matches first.
select productId,
count(case when attributeName = 'Height' and attributeValue='3' then 1 end)
+ count(case when attributeName = 'Weight' and attributeValue='1' then 1 end)
+ count(case when attributeName = 'Category' and attributeValue='C1' then 1 end) as rank
from mytable
group by productId
order by rank desc
The query above returns all rows even with 0 matches. If you only want to return rows with 1 or more matches, then use the query below, which should be able to take advantage of your composite index:
select productId, count(*) as rank
from mytable
where (attributeName = 'Height' and attributeValue = '3')
or (attributeName = 'Weight' and attributeValue = '1')
or (attributeName = 'Category' and attributeValue = 'C1')
group by productId
order by rank desc