From SQL table find the same product have same product key

Question

I have table in the following structure, I need to write SQL to find the product having multiple product keys? Can anyone please help to write the SQL?

Product	Product Key
First	10
First	1
Second	2
Second	2
Third	3
Four	3
Test	5
Test	5

Expected output would be

Product
First
Third
Four

Answer 1

This is how you get using syntax from SQL Server

SELECT Product
FROM Products
WHERE "Product Key" IN (
    SELECT "Product Key"
    FROM Products
    GROUP BY "Product Key"
    HAVING COUNT(DISTINCT Product) > 1
)
GROUP BY Product;

These are the steps:

1. You have to search product key that contain multiple product.
2. We have 1 and 3.
3. And then we get product that has product key = 1 and 3.
4. Then, we will get this output:

This is fiddle for sql server.

You can adjust it to monetdb syntax