100.View the Exhibit and examine the structure of the PROMOTIONS table.

100.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
解析：
decode(expr,search,result[,search,result,...,default]),比较expr和search，如果匹配返回result，如果都不匹配返回default
如果没有default那么返回null,oracle会将expr和匹配到的search,或者default自动转换为第一个result的类型，如果第一个result为char类型，那么返回varchar2类型
A:正确
B:正确
C:错误,如果NULLIF(promo_cost, 10000)返回不是null，那么最后结果应该是'N/A',他应该转换为第一个result，也就是promo_cost*.25，转换失败
D:错误，decode 里面 >100这个错误