单选题Examine the description of the EMPLOYEES table: EMP_ID NUMBER(4) NOT NULL LAST_NAME VARCHAR2(30) NOT NULL FIRST_NAME VARCHAR2(30) DEPT_ID NUMBER(2) Which statement produces the number of different departments that have employees with last name Smith?（）
题目
单选题
Examine the description of the EMPLOYEES table: EMP_ID NUMBER(4) NOT NULL LAST_NAME VARCHAR2(30) NOT NULL FIRST_NAME VARCHAR2(30) DEPT_ID NUMBER(2) Which statement produces the number of different departments that have employees with last name Smith?（）
A
SELECT COUNT (*) FROM employees WHERE last _name='smith';
B
SELECT COUNT (dept_id) FROM employees WHERE last _name='smith';
C
SELECT DISTINCT (COUNT (dept_id) FROM employees WHERE last _name='smith';
D
SELECT COUNT (DISTINCT dept_id) FROM employees WHERE last _name='smith';
E
SELECT UNIQE (dept_id) FROM employees WHERE last _name='smith';