105. Examine the structure of the PROMOS table:

name              Null        Type

PROMO_ID          NOT NULL    NUMBER(3)

PROMO_NAME                   VARCHAR2(30)

PROMO_START_DATE NOT NULL    DATE

PROMO_END_DATE    NOT NULL    DATE

You want to display the list of promo names with the message 'Same Day' for promos that started and

ended on the same day.

Which query gives the correct output?

A. SELECT promo_name, NVL(NULLIF(promo_start_date, promo_end_date), 'Same Day') FROM promos;

B. SELECT promo_name, NVL(TRUNC(promo_end_date - promo_start_date), 'Same Day') FROM promos;

C. SELECT promo_name, NVL2(TO_CHAR(TRUNC(promo_end_date-promo_start_date)), NULL,'Same

Day') FROM promos;

D. SELECT promo_name, DECODE((NULLIF(promo_start_date, promo_end_date)), NULL,'Same day') FROM promos;

Answer: D

答案解析：

A。NULLIF裡面額資料型別為date與 'Same Day'字串型別不匹配，錯誤。

B。TRUNC將小數部分截斷，但型別不一致，錯誤。

C。TO_CHAR(TRUNC(promo_end_date-promo_end_date))，如果相等，TRUNC為0，to_char後，字元為0，即始終有值，NVL2返回第二個值，即NULL

 

[email protected]>  SELECT promo_name, NVL2(TO_CHAR(TRUNC(promo_end_date-promo_end_date)), NULL,'SameDay') FROM PROMOTIONS;

 

PROMO_NAME                     NVL2(TO

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

NO PROMOTION #

newspaper promotion #16-108

post promotion #20-232

newspaper promotion #16-349

internet promotion #14-471

D。實驗驗證：正確的。 [email protected]> SELECT  DECODE((NULLIF('11-mon-01','11-mon-01')),null,'same') from dual;   DECO ---- same

 

[email protected]> SELECT  DECODE(null,null,'same') from dual;   DECO ---- same  

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