OCP-1Z0-051-V9 02-100題
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;
Answer: AB 答案解析: 參考: http://blog.csdn.net/rlhua/article/details/12868497 http://blog.csdn.net/rlhua/article/details/12860467C不正確,因為把’N/A’隱式轉換成數值時不成功。D語法不正確。
DECODE(expr,search1,result1[,search2,result2……,default]):比較expr與search,如果等於search1則返回result1,如果等於search2則返回result2,依次類推,如果都不等於,如果有default則返回default,否則返回NULL.
ORACLE在比較之前,會自動把expr和每一個search隱式轉換成第一個search(search1)的資料型別。自動把返回值轉換成第一個result(result1)的資料型別。如果第一個result的資料型別為CHAR或者值是null,則Oracle轉換返回值為VARCHAR2.
在DECODE函式中,NULL是相等的,如果expr為空,則Oracle將會返回第一個為NULL的search所對應的result。DECODE列表中的最大表達式個數為255個。
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