50、(11-15)choose two

Examine the structure of the MARKS table:

Which two statements would execute successfully?

A) SELECT SUM(subjectl+subject2+subject3)

FROM marks

WHERE student_name IS NULL;

B) SELECT SUM(DISTINCT NVL(subject1,0)), MAX(subjectl)

FROM marks

WHERE subjectl > subject2;

C) SELECT student_name,subjectl

FROM marks

WHERE subjectl > AVG(subjectl);

D) SELECT student_name, SUM (subjectl)

FROM marks

WHERE student_name LIKE 'R%';

Answer：AB

(解析：C 答案 where 子句中用到了 avg 函数，必须用 having;D 答案 student_name 没有在 group by 子句中出现。

B 答案可以写成如下方式运行：

SELECT SUM(DISTINCT NVL(comm,0)), MAX(sal)

FROM emp

WHERE sal > comm;

)