单项选择题
You own a table called EMPLOYEES with this table structure:
EMPLOYEE_ID NUMBER Primary Key
FIRST_NAME VARCHAR2(25)
LAST_NAME VARCHAR2(25)
HIRE_DATE DATE
What happens when you execute this DELETE statement?
DELETE employees;（）
A.You get an error because of a primary key violation.
B.The data and structure of the EMPLOYEES table are deleted.
C.The data in the EMPLOYEES table is deleted but not the structure.
D.You get an error because the statement is not syntactically correct.
相关考题
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单项选择题
The CUSTOMERS table has these columns: CUSTOMER_ID NUMBER(4) NOT NULL CUSTOMER_NAME VARCHAR2(100) NOT NULL STREET_ADDRESS VARCHAR2(150) CITY_ADDRESS VARCHAR2(50) STATE_ADDRESS VARCHAR2(50) PROVINCE_ADDRESS VARCHAR2(50) COUNTRY_ADDRESS VARCHAR2(50) POSTAL_CODE VARCHAR2(12) CUSTOMER_PHONE VARCHAR2(20) The CUSTOMER_ID column is the primary key for the table. You need to determine how dispersed your customer base is. Which expression finds the number of different countries represented in the CUSTOMERS table?（）
A.COUNT(UPPER(country_address))
B.COUNT(DIFF(UPPER(country_address)))
C.COUNT(UNIQUE(UPPER(country_address)))
D.COUNT DISTINCT UPPER(country_address)
E.COUNT(DISTINCT (UPPER(country_address))) -
单项选择题
Which statement adds a constraint that ensures the CUSTOMER_NAME column of the CUSTOMERS table holds a value?（）
A.ALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;
B.ALTER TABLE customers MODIFY CONSTRAINT cust_name_nn CHECK customer_name IS NOT NULL;
C.ALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn NOT NULL;
D.ALTER TABLE customers MODIFY customer_name CONSTRAINT cust_name_nn IS NOT NULL;
E.ALTER TABLE customers MODIFY name CONSTRAINT cust_name_nn NOT NULL;
F.ALTER TABLE customers ADD CONSTRAINT cust_name_nn CHECK customer_name NOT NULL; -
多项选择题
Click the Exhibit button and examine the data from the EMP table. The COMMISSION column shows the monthly commission earned by the employee. Which two tasks would require subqueries or joins in order to be performed in a single step? （）
A.listing the employees who earn the same amount of commission as employee 3
B.finding the total commission earned by the employees in department 10
C.finding the number of employees who earn a commission that is higher than the average commission of the company
D.listing the departments whose average commission is more than 600
E.listing the employees who do not earn commission and who are working for department 20 in descending order of the employee ID
F.listing the employees whose annual commission is more than 6000
