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102. Examine the structure of the TRANSACTIONS table:

name            Null            Type

TRANS_ID        NOT NULL        NUMBER(3)

CUST_NAME                      VARCHAR2(30)

TRANS_DATE                     TIMESTAMP

TRANS_AMT  NUMBER(10,2)

You want to display the date, time, and transaction amount of transactions that where done before 12

noon. The value zero should be displayed for transactions where the transaction amount has not been

entered.

Which query gives the required result?

A. SELECT TO_CHAR(trans_date,'dd-mon-yyyy hh24:mi:ss'),

TO_CHAR(trans_amt,'$99999999D99')

FROM transactions

WHERE TO_NUMBER(TO_DATE(trans_date,'hh24')) < 12 AND COALESCE(trans_amt,NULL)<>NULL;    

B. SELECT TO_CHAR(trans_date,'dd-mon-yyyy hh24:mi:ss'), 

NVL(TO_CHAR(trans_amt,'$99999999D99'),0)

FROM transactions

WHERE TO_CHAR(trans_date,'hh24') < 12;

C. SELECT TO_CHAR(trans_date,'dd-mon-yyyy hh24:mi:ss'), 

COALESCE(TO_NUMBER(trans_amt,'$99999999.99'),0)  已經是number型別，不需要轉換

FROM transactions

WHERE TO_DATE(trans_date,'hh24') < 12;

D. SELECT TO_DATE (trans_date,'dd-mon-yyyy hh24:mi:ss'), 

NVL2(trans_amt,TO_NUMBER(trans_amt,'$99999999.99'), 0)  已經是number型別，不需要轉換

FROM transactions

WHERE TO_DATE(trans_date,'hh24') < 12;

Answer: B

答案解析：

A,TO_DATE(trans_date,'hh24')，trans_date已經為日期型別，不用再to_date

[email protected]> select to_date(HIREDATE,'yy24') from emp; select to_date(HIREDATE,'yy24') from emp                         * ERROR at line 1: ORA-01821: date format not recognized

B,正確，這裡0隱式轉換為字元型

C,(TO_NUMBER(trans_amt,'$99999999.99')，trans_amt已經是數值型，不用再to_number

D,錯誤同C一樣。

 

           

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