In Case Study #1: Danny's Diner it should be using row_number instead of dense_rank in below question due to which 2 products are displayed because of dense_rank

[shubhamphegade]

@katiehuangx --3. What was the first item from the menu purchased by each customer? WITH ordered_sales_cte AS

(

SELECT 
customer_id, 
order_date, 
product_name,
    row_number() OVER(PARTITION BY s.customer_id ORDER BY s.order_date) AS rank
FROM dbo.sales AS s
JOIN dbo.menu AS m
    ON s.product_id = m.product_id

)

SELECT customer_id, product_name FROM ordered_sales_cte WHERE rank = 1 GROUP BY customer_id, product_name;

--Using dense_rank:

--Using row_number(correct one):

[jegazhu]

Great sharing, thanks.

[raghavbansal99]

Since both 'sushi' and 'curry' are puchased on the same day (2021-01-01), they should both be included

[katiehuangx]

The order_date field does not have a timestamp, hence it is impossible to determine the exact sequence of items ordered by the customer.

Therefore, it would be inaccurate to conclude that curry is the customer's first order purely based on the alphabetical order of the product names.

For this reason, I maintain my solution of using DENSE_RANK() and consider both curry and sushi as Customer A's first order.