单项选择题
A.SELECT city_address, COUNT(*) FROM customers WHERE city_address IN ('Los Angeles', 'San Francisco');
B.SELECT city_address, COUNT(*) FROM customers WHERE city_address IN ('Los Angeles', 'San Francisco') GROUP BY city_address;
C.SELECT city_address, COUNT(customer_id) FROM customers WHERE city_address IN ('Los Angeles', 'San Francisco') GROUP BY city_address, customer_id;
D.SELECT city_address, COUNT(customer_id) FROM customers GROUP BY city_address IN ('Los Angeles', 'San Francisco');
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); Which is true about your ALTER statement?（）
单项选择题 Click the Exhibit button to examine the data of the EMPLOYEES table. Which statement lists the ID, name, and salary of the employee, and the ID and name of the employees manager, for all the employees who have a manager and earn more than 4000?（）
单项选择题 A subquery can be used to（）.