单项选择题 You would like to display the system date in the format "Monday, 01 June, 2001".Which SELECT statement should you use?（）

单项选择题 Evaluate these two SQL statements: SELECT last_name, salary , hire_date FROM EMPLOYEES ORDER BY salary DESC; SELECT last_name, salary, hire_date FROM EMPLOYEES ORDER BY 2 DESC; What is true about them?（）

单项选择题 Examine the data in the EMPLOYEES table. EMPLOYEES EMP_NAME DEPT_ID MGR_ID JOB_ID SALARY EMPLOYEE_ID 101 Smith 20 120 SA_REP 4000 102 Martin 10 105 CLERK 2500 103 Chris 20 120 IT_ADMIN 4200 104 John 30 108 HR_CLERK 2500 105 Diana 30 108 IT_ADMIN 5000 106 Smith 40 110 AD.ASST 3000 108 Jennifer 30 110 HR_DIR 6500 110 Bob 40 EK_DIR 8000 120 Revi 20 110 SA_DIR 6500 On the EMPLOYEES table, EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID. The JOB_ID column is a NOT NULL column. Evaluate this DELETE statement: DELETE employee_id, salary, job_id FROM employees WHERE dept_id = 90; Why does the DELETE statement fail when you execute it?（）