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) 已经是number类型，不需要转换
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) 已经是number类型，不需要转换
FROM transactions
WHERE TO_DATE(trans_date,'hh24') < 12;
Answer: B
答案解析：
A,TO_DATE(trans_date,'hh24')，trans_date已经为日期类型，不用再to_date
B,正确，这里0隐式转换为字符型
C,(TO_NUMBER(trans_amt,'$99999999.99')，trans_amt已经是数值型，不用再to_number
D,错误同C一样。