ocp题库解析：11g-1Z0-051-第6题
ocp题库解析：11g-1Z0-051-第6题，完整题库请点击这里联系老师咨询了解
6. Examine the structure of the SHIPMENTS table:
name Null Type
PO_ID NOT NULL NUMBER(3)
PO_DATE NOT NULL DATE
SHIPMENT_DATE NOT NULL DATE
SHIPMENT_MODE VARCHAR2(30)
SHIPMENT_COST NUMBER(8,2)
You want to generate a report that displays the PO_ID and the penalty amount to be paid if the
SHIPMENT_DATE is later than one month from the PO_DATE. The penalty is $20 per day.
Evaluate the following two queries:
SQL> SELECT po_id, CASE
WHEN MONTHS_BETWEEN (shipment_date,po_date)>1 THEN
TO_CHAR((shipment_date - po_date) * 20) ELSE 'No Penalty' END PENALTY
FROM shipments;
SQL>SELECT po_id, DECODE
(MONTHS_BETWEEN (po_date,shipment_date)>1,
TO_CHAR((shipment_date - po_date) * 20), 'No Penalty') PENALTY
FROM shipments;
Which statement is true regarding the above commands?
A. Both execute successfully and give correct results.
B. Only the first query executes successfully but gives a wrong result.
C. Only the first query executes successfully and gives the correct result.
D. Only the second query executes successfully but gives a wrong result.
E. Only the second query executes successfully and gives the correct result.
Answer: C
答案解析：
题意要求： 显示PO_ID和支付的罚款总金额，SHIPMENT_DATE与PO_DATE进行比较，SHIPMENT_DATE如果比PO_DATE晚一个月，则每天罚款$20。
MONTHS_BETWEEN(date1, date2): 返回date1和date2两个日期之间间隔几个月，结果可以为正或为负。如果date1晚于date2则结果为正;如果date1早于date2则结果为负;结果的非整数部分也代表月间隔的一部分。
DECODE(expr,search1,result1[,search2,result2……,default])：比较expr与search，如果等于search1则返回result1，如果等于search2则返回result2，依次类推，如果都不等于，如果有default则返回default，否则返回NULL.
ORACLE在比较之前，会自动把expr和每一个search隐式转换成第一个search(search1)的数据类型。自动把返回值转换成第一个result(result1)的数据类型。如果第一个result的数据类型为CHAR或者值是null，则Oracle转换返回值为VARCHAR2.
在DECODE函数中,NULL是相等的，如果expr为空，则Oracle将会返回第一个为NULL的search所对应的result。DECODE列表中的最大表达式个数为255个。
第一个SQL的表达是正确，可以正确执行的。其实我觉得这道题的答案有点出入，MONTHS_BETWEEN返回的是月数，每天罚款$20，相乘起来，因为一个是天的单位，一个是月的单位，如果题中改成每月罚款20，则才是正确的。
DECODE 的表达是错误的。
sh@TEST0924> SELECT po_id, DECODE (MONTHS_BETWEEN (po_date,shipment_date)>1,
2 TO_CHAR((shipment_date - po_date) * 20), 'No Penalty') PENALTY
3 FROM shipments;
SELECT po_id, DECODE (MONTHS_BETWEEN (po_date,shipment_date)>1,
*
ERROR at line 1:
ORA-00907: missing right parenthesis
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