多项选择题
A. DELETE employees;
B. DESCRIBE employees;
C. ROLLBACK TO SAVE POINT C;
D. GRANT SELECT ON employees TO SCOTH
E. ALTER TABLE employees SET UNUSED COLUMN sal;
F. Select MAX(sal) FROM employees WHERE department _ id 20;
单项选择题 The DBA issues this SQL command: CREATE USER scott IDENTIFIES by tiger; What privileges does the user Scott have at this point? （）
单项选择题 The EMPLOYEES table has these columns: LAST NAME VARCHAR2(35) SALARY NUMBER(8,2) HIRE_DATE DATE Management wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement: ALTER TABLE EMPLOYEES MODIFY ( SALARY DEFAULT 5000); What is true about your ALTER statement?（）
单项选择题 Which substitution variable would you use if you want to reuse the variable without prompting the user each time? （）