SQL select command:
9. List the part number, part description, and on-hand value for each part whose on-hand value is at least $7,500. Assign the name ON_HAND VALUE to the computation.
18. What is the part number, description,and price of the most expensive part in the database? (Hint: Use a subquery.)

19. List the sum of the balances of all customers for each sales rep. Order and group the results by sales rep number.

20. List the sum of the balances of all customers for each sales rep, but restrict the output to those sales reps for whom the sum is more than $10,000.

21. List the part number of any part with an unknown description.


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把表结构写出来...