query: SELECT product_id ,  count(DISTINCT order_id) FROM Order_items GROUP BY product_id
question: How many distinct orders ids corresponds to each products?
query_toks: SELECT product_id , count ( DISTINCT order_id ) FROM Order_items GROUP BY product_id
query_toks_no_value: select product_id , count ( distinct order_id ) from order_items group by product_id
question_toks: How many distinct orders ids corresponds to each products?