ocp 11g考試題庫詳解：1Z0-051-104題，完整題庫請點擊這里聯系老師咨詢了解

104. 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 DATE

You want to generate a report showing promo names and their duration (number of days). If the

PROMO_END_DATE has not been entered, the message 'ONGOING' should be displayed.

Which queries give the correct output? (Choose all that apply.)

A. SELECT promo_name, TO_CHAR(NVL(promo_end_date -promo_start_date,'ONGOING'))

FROM promos;

B. SELECT promo_name,COALESCE(TO_CHAR(promo_end_date - promo_start_date),'ONGOING')

FROM promos;

C. SELECT promo_name, NVL(TO_CHAR(promo_end_date -promo_start_date),'ONGOING')

FROM promos;

D. SELECT promo_name, DECODE(promo_end_date -promo_start_date,NULL,'ONGOING',promo_end_date - promo_start_date)

FROM promos;

E. SELECT promo_name, decode(coalesce(promo_end_date,promo_start_date),null,'ONGOING',

promo_end_date - promo_start_date)

FROM promos;

Answer: BCD

試題解析：

ANVL要求括號內參數的類型需一致，,NVL(promo_end_date -promo_start_date,'ONGOING')此處類型不一致，一個為數值型，一個為字符型

B, COALESCE 需括號內參數類型需一致，TO_CHAR(promo_end_date - promo_start_date),'ONGOING') ，此處使用to_char轉換，兩個參數都為字符型，可以比較。正確。

C, NVL(TO_CHAR(promo_end_date -promo_start_date),'ONGOING')，NVL括號內兩個參數都為字符型，正確。

D,表達式正確

E,不滿足題意，coalesce返回第一個不為空的值，因為promo_start_date肯定不為空，所以即使promo_end_date為空，coalesce也會返回promo_start_dat，所以都會顯示promo_end_date - promo_start_date值，即當promo_end_date為空時，還是會顯示空(注意，如果你直接指定NULL-sysdate會報轉換數據類型錯，而在字段里就可以減，并返回空。