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Evaluate these two SQL statements: SELECT last_name, salary , hire_date FROM EMPLOYEES ORDER BY salary DESC; SELECT last_name, salary, hire_date FROM EMPLOYEES ORDER BY 2 DESC; What is true about them? （）
A:The two statements produce identical results.
B:The second statement returns a syntax error.
C:There is no need to specify DESC because the results are sorted in descending order by default.
D:The two statements can be made to produce identical results by adding a column alias for the salary column in the second SQL statement.

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出自：Oracle认证

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