单项选择题
A. ALTER TABLE student_grades ADD FOREIGN KEY (student_id) REFERENCES students(student_id);
B. ALTER TABLE student_grades ADD CONSTRAINT NAME = student_id_fk FOREIGN KEY (student_id) REFERENCES students(student_id);
C. ALTER TABLE student_grades ADD CONSTRAINT student_id_fk FOREIGN KEY (student_id) REFERENCES students(student_id);
D. ALTER TABLE student grades ADD NAMED CONSTRAINT student_id_fk FOREIGN KEY (student_id) REFERENCES students(student_id);
E. ALTER TABLE student grades ADD NAME student_id_fk FOREIGN KEY (student_id) REFERENCES students(student_id);
单项选择题 You want to display the titles of books that meet these criteria: 1. Purchased before January 21, 2001 2. Price is less then $500 or greater than $900 You want to sort the results by their data of purchase, starting with the most recently bought book. Which statement should you use?（）
多项选择题 Which two are true about aggregate functions? （）
单项选择题 Which /SQL*Plus feature can be used to replace values in the WHERE clause?（）