LeetCode 586 challenges developers to identify the customer number that has placed the highest volume of orders. The problem presents an orders table with two identifiers: order_number and customer_number. Solvers must return a single customer, though a follow‑up asks how to handle ties.

The solution splits into two CTEs. First, customer_order_count aggregates rows with GROUP BY and COUNT(order_number) to compute each customer's order total. Second, customer_order_rank applies RANK() OVER (ORDER BY order_count DESC), assigning rank 1 to the highest counts and preserving ties.

Implemented in PostgreSQL, the query uses the OVER keyword to instruct the engine on the ranking scope. By omitting PARTITION BY, the function evaluates the entire result set, ensuring that any tied customers receive the same top rank. The final SELECT filters for order_rnk = 1.

This pattern is common in interview coding tests and real‑world data analysis, where ranking tied groups matters. Practicing with window functions sharpens SQL fluency and prepares developers for production scenarios. Future challenges may ask for top‑N customers or aggregate metrics across multiple dimensions.