The solution above is optimal because it uses the ORDER BY and LIMIT clauses to sort the table by value in descending order and then return the first row.
The candidate's solution is correct and demonstrates a good understanding of SQL. The solution is optimal, using the ORDER BY and LIMIT clauses to sort the table by total_spend in descending order and then limit the results to the top 10 customers.
This solution is correct and demonstrates a level of completeness. It correctly calculates the sum of the values in table A and table B, and then multiplies them together.
The solution above is optimal because it uses the COUNT function with the DISTINCT keyword. This will count the number of unique values in each column.