单项选择题 The user Alice wants to grant all users query privileges on her DEPT table. Which SQL statement accomplishes this?（）

单项选择题 Examine the structure of the EMPLOYEES table: EMPLOYEE_ID NUMBER NOT NULL EMP_NAME VARCHAR2(30) JOB_ID VARCHAR2(20) SAL NUMBER MGR_ID NUMBER DEPARTMENT_ID NUMBER You want to create a SQL script file that contains an INSERT statement. When the script is run, the INSERT statement should insert a row with the specified values into the EMPLOYEES table. The INSERT statement should pass values to the table columns as specified below: EMPLOYEE_ID: Next value from the sequence EMP_ID_SEQEMP_NAME and JOB_ID: As specified by the user during run time, through substitution variables SAL: 2000 MGR_ID: No value DEPARTMENT_ID: Supplied by the user during run time through substitution variable. The INSERT statement should fail if the user supplies a value other than 20 or 50. Which INSERT statement meets the above requirements?（）

单项选择题 Which constraint can be defined only at the column level?（）