单项选择题
A. SELECT customer_id, customer_name FROM customers WHERE postal_code CONTAINS NULL;
B. SELECT customer_id, customer_name FROM customers WHER postal_code = ' ___________';
C. SELECT customer_id, customer_name FROM customers WHERE postal _ code IS NULL;
D. SELECT customer_id, customer_name FROM customers WHERE postal code IS NVL;
E. SELECT customer_id, customer_name FROM customers WHERE postal_code = NULL;
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 The EMP table has these columns: ENAME VARCHAR2(35) SALARY NUMBER(8,2) HIRE_DATE DATE Management wants a list of names of employees who have been with the company for more than five years. Which SQL statement displays the required results? （）