Question

I’ve a scenario in Sql where I’ve following schema.

If I have 3 items in the Item table then one unique combination of all the items will be assigned to a user. For ex:

Items:
1
2
3

Then combinations will be: {1}, {2}, {3}, {1,2}, {1,2,3}, {1,3}, {2,3) all are unique combinations.
Any of these combination will be assigned to a single user.

Now I want to find out given combination belongs to which user, how can I find that? For ex: I’ll pass items list {2,3} then it should return the userid who is having that combination from the table UserItemCombinations. {2,3} is passed as comma separated string to a SP. I’ve taken 3 items as example, this table may contain n number of items. Users number will be dependent on the number of combinations. For ex: For three items there are 7 combinations so 7 users will be there user table.

Answer 1

UserItemCombinations will have one row for each user-item, and one user can have only one combination, so if the query combination is {2,3}

select userid from user where userid not in 
  (select distinct userid from UserItemCombinations where itemid in 
                 (select itemid from item where itemid not in (2,3));