单项选择题
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 UNIQUE(dept_id) FROM employees WHERE last_name='Smith';
相关考题
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多项选择题
Which three statements about subqueries are true? （）
A.A single row subquery can retrieve only one column and one row.
B.A single row subquery can retrieve only one row but many columns.
C.A multiple row subquery can retrieve multiple rows and multiple columns.
D.A multiple row subquery can be compared using the ">" operator.
E.A single row subquery can use the IN operator.
F.A multiple row subquery can use the "=" operator. -
单项选择题
Click the Exhibit button and examine the data in the EMPLOYEES table. On the EMPLOYEES table, EMPLOYEE_ID is the primary key. MGR_ID is the ID of managers and refers to the EMPLOYEE_ID. The JOB_ID column is a NOT NULL column. Evaluate this DELETE statement: DELETE employee_id, salary, job_id FROM employees WHERE dept_id = 90; Why does the DELETE statement fail when you execute it?（）
A.There is no row with dept_id 90 in the EMPLOYEES table.
B.You cannot delete the JOB_ID column because it is a NOT NULL column.
C.You cannot specify column names in the DELETE clause of the DELETE statement.
D.You cannot delete the EMPLOYEE_ID column because it is the primary key of the table. -
多项选择题
Examine the description of the STUDENTS table: STD_ID NUMBER(4) COURSE_ID VARCHAR2(10) START_DATE DATE END_DATE DATE Which two aggregate functions are valid on the START_DATE column? （）
A.SUM(start_date)
B.AVG(start_date)
C.COUNT(start_date)
D.AVG(start_date, end_date)
E.MIN(start_date)
F.MAXIMUM(start_date)
