OCP-1Z0-051 第100题 DECODE,NULLIF函数用法

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一、原题

View the Exhibit and examine the structure of the PROMOTIONS table.
Which SQL statements are valid? (Choose all that apply.)
A. SELECT promo_id, DECODE(NVL(promo_cost,0), promo_cost,promo_cost * 0.25, 100) "Discount"
        FROM promotions;
B. SELECT promo_id, DECODE(promo_cost, 10000,DECODE(promo_category, 'G1', promo_cost *.25, NULL),NULL) "Catcost"
        FROM promotions;
C. SELECT promo_id, DECODE(NULLIF(promo_cost, 10000),NULL, promo_cost*.25, 'N/A') "Catcost"
        FROM promotions;
D. SELECT promo_id, DECODE(promo_cost, >10000, 'High',<10000, 'Low') "Range"
        FROM promotions;

答案：AB

二、题目翻译

查看 PROMOTIONS 表的结构
选择所有有效的SQL语句（选择所有正确的选项）。

三、题目解析

C选项不正确，前面几个参数都是number类型，最后一个是字符类型，隐式转换数值时不成功。
D选项语法不正确。

NVL和NULLIF的用法，详见：
http://blog.csdn.net/holly2008/article/details/25251513

DECODE的用法，详见：
http://blog.csdn.net/holly2008/article/details/23140591

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