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;
多项选择题 Examine the structure of the EMPLOYEES, DEPARTMENTS, and LOCATIONS tables. Which two SQL statements produce the name, department name, and the city of all the employees who earn more then 10000?（）
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?（）