Descriptions:

This query uses CTEs (WITH clauses) to build two result sets and then combines them with UNION:

• subs CTE: aggregates the orders table to compute, for each customer_id, how many subscriptions they have (COUNT(subscription_id)), labeled as nbr_of_subscriptions.
• tony_subs CTE: creates a manual/constant row that represents a customer named Tony with 5 subscriptions (useful for testing or appending a special-case row).
• Final SELECT:
  • Joins subs with customers to output each customer’s name and their computed subscription count.
  • Uses UNION to append the Tony row from tony_subs to the end of the results.

Result: a list of customers with their number of subscriptions, plus an extra row: Tony | 5.