单项选择题
You added a PHONE_NUMBER column of NUMBER data type to an existing EMPLOYEES table. The EMPLOYEES table already contains records of 100 employees. Now, you want to enter the phone numbers of each of the 100 employees into the table. Some of the employees may not have a phone number available. Which data manipulation operation do you perform?（）
A. MERGE B. INSERT C. UPDATE D. ADD E. ENTER F. You cannot enter the phone numbers for the existing employee records.
单项选择题 What does the TRUNCATE statement do?（）
单项选择题 Which is an /SQL*Plus command?（）
单项选择题 Examine the data of the EMPLOYEES table. EMPLOYEES (EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID) Evaluate this SQL statement: What is its output?（）
