（113）Examine the structure of the ORDERS table:

Name Null Type

ORDER_ID NOT NULL NUMBER(12)

ORDER_DATE NOT NULL TIMESTAMP(6)

CUSTOMER_ID NOT NULL NUMBER(6)

ORDER_STATUS NUMBER(2)

ORDER_TOTAL NUMBER(8,2)

You want to find the total value of all the orders for each year and issue the following command:

SELECT TO_CHAR(order_date,'rr'), SUM(order_total)

FROM orders

GROUP BY TO_CHAR(order_date,'yyyy');

Which statement is true regarding the outcome?

A. It executes successfully and gives the correct output.

B. It gives an error because the TO_CHAR function is not valid.

C. It executes successfully but does not give the correct output.

D. It gives an error because the data type conversion in the SELECT list does not match the data type conversion in the GROUP BY clause.

答案：（D）

解析：

scott@TESTDB11>select to_char(hiredate, 'rr'), sum(sal)

2 from emp

3 group by to_char(hiredate, 'yyyy');

select to_char(hiredate, 'rr'), sum(sal)

*

ERROR at line 1:

ORA-00979: not a GROUP BY expression

--要求没有出现在聚合函数中的列,必须出现在group by子句中,而且形式必须一致

scott@TESTDB11>select to_char(hiredate, 'rr'), sum(sal)

2 from emp

3 group by to_char(hiredate, 'rr');

TO SUM(SAL)

-- ----------

87 5100

81 22925

82 1300

80 1800

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OCP 1Z0-051-113