Given a dataset with two columns, cartId (session ID) and items (an array of items added to the cart), the Marketing team requests a unique list of items ever added to the cart by each customer. Complete the query to achieve the expected result.

Schema: cartId INT, items Array

Sample Data:

SELECT cartId, ___ (___(items)) as items
FROM carts GROUP BY cartId

Expected result:

cartId          items
1               [1,100,200,300,250]