¨ Always take note when computing aggregates of
aggregates!
“Find the largest total account balance of any branch.”
🞑 Two nested aggregates: max of sums
¨ A very common mistake:
SELECT branch_name, SUM(balance) AS tot_bal
FROM account GROUP BY branch_name
HAVING tot_bal = MAX(tot_bal)
🞑 A SELECT query can only perform one level of aggregation
🞑 Need a second SELECT to find the maximum total
🞑 Unfortunately, MySQL accepts this and returns bogus result
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