Question

I have a table Named ProductLike with the fields ProductId, UserId, and Like. When a user likes a product, a record is added to this table with the UserId and ProductId, as well as the Like value (true or false). I want to get a list or group of users who have each product. This is what I have tried so far, but it has errors.

SELECT  p.UserId,* 
FROM    ProductLike p WHERE p.ProductId =
        (SELECT pk.ProductId FROM ProductLike pk WHERE pk.ProductLike = 1);

Answer 1

You can alias the table and join like so:

SELECT p.ProductId,p.UserId,p2.UserId 
FROM ProductLike p 
JOIN ProductLike p2 ON p.ProductId = p2.ProductId
WHERE p.[Like]=1 AND p2.[Like]=1 
  AND p.UserId <> p2.UserId

This will give you a result set of all users who have “liked” the same product.

EDIT: If you wanted to get a result set of all products that have been liked more than once, you could do this:

SELECT p.ProductId, COUNT(p.ProductId) 'Likes'
FROM ProductLike p 
WHERE p.[Like]=1 
GROUP BY p.ProductId
HAVING COUNT(p.ProductId) > 1