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Exhibit The COMMISSION column shows the monthly commission earned by the employee. Which two tasks would require subqueries or joins in order to be performed in a single step? （）
A:listing the employees who earn the same amount of commission as employee 3
B:finding the total commission earned by the employees in department 10
C:finding the number of employees who earn a commission that is higher than the average commission of the company
D:listing the departments whose average commission is more that 600
E:listing the employees who do not earn commission and who are working for department 20 in descending order of the employee ID 
F:listing the employees whose annual commission is more than 6000

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出自：Oracle认证

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