added mock interview problem.

[krishnadheerajkrovi]

Please review

[super30admin]

The solution demonstrates a solid understanding of the problem using a Common Table Expression (CTE) approach. The logic is sound: finding the minimum year per product and then joining back to get all sales from that first year. The comments are helpful for understanding the approach. However, there are some areas for improvement: the query doesn't include a primary ordering requirement (if the problem expects ordered results), and while the solution handles the core logic correctly, it could benefit from more explicit column selection and potential edge case handling (like products with no sales).