OCP-1Z0-051-V9.02-88题

88. You need to calculate the number of days from 1st January 2007 till date.

Dates are stored in the default format of dd-mon-rr. 

Which SQL statements would give the required output? (Choose two .)

A. SELECT SYSDATE - '01-JAN-2007' FROM DUAL;

B. SELECT SYSDATE - TO_DATE('01/JANUARY/2007') FROM DUAL;

C. SELECT SYSDATE - TO_DATE('01-JANUARY-2007') FROM DUAL;

D. SELECT TO_CHAR(SYSDATE, 'DD-MON-YYYY') - '01-JAN-2007' FROM DUAL;

E. SELECT TO_DATE(SYSDATE, 'DD/MONTH/YYYY') - '01/JANUARY/2007' FROM DUAL;

Answer: BC

 答案解析：

参考： http://blog.youkuaiyun.com/rlhua/article/details/12832885

日期与字符串做表达式计算，隐式将日期转换为字符串，而字符串之间不能相减，所以ADE都是字符之间相减，所以错误。

BC之间相减是日期与日期之间的减，得出数字，是正确的。