（155）Evaluate the following SQL statement:

SELECT promo_id, promo_category FROM promotions WHERE promo_category = 'Internet' ORDER BY 2 DESC

UNION

SELECT promo_id, promo_category FROM promotions WHERE promo_category = 'TV'

UNION

SELECT promo_id, promo_category FROM promotions WHERE promo_category ='Radio'

Which statement is true regarding the outcome of the above query?

A. It executes successfully and displays rows in the descending order of PROMO_CATEGORY.

B. It produces an error because positional notation cannot be used in the ORDER BY clause with SET operators.

C. It executes successfully but ignores the ORDER BY clause because it is not located at the end of the compound statement.

D. It produces an error because the ORDER BY clause should appear only at the end of a compound query-that is, with the last SELECT statement.

答案：（D）

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