多项选择题
A.SELECT SUM(subj1, subj2, subj3) FROM marks;
B.SELECT SUM(subj1 + subj2 + subj3) FROM marks;
C.SELECT SUM(subj1), SUM(subj2), SUM(subj3) FROM marks;
D.SELECT MAX(subj1, subj2, subj3) FROM marks;
E.SELECT MINIMUM(subj1) FROM marks;
F.SELECT COUNT(std_id) FROM marks WHERE subj1 >= AVG(subj1);
单项选择题 Examine the description of the EMPLOYEES table: Which statement produces the number of different departments that have employees with last name Smith?（）
单项选择题 Which SELECT statement should you use to extract the year from the system date and display it in the format "1998"?（）
单项选择题 In which scenario would an index be most useful?（）