choose two.
You need to calculate the number of days from 1st January 2019 until today.
Dates are stored in the default format of DD-MON-RR.
Which two queries give the required output?
A) SELECT SYSDATE - TO_DATE (' 01-JANUARY-2019' ) FROM DUAL;
B) SELECT TO_DATE (SYSDATE, ' DD/MONTH/YYYY' ) - '01/JANUARY/2019' FROM DUAL;
C) SELECT ROUND (SYSDATE - TO_DATE(' 01/JANUARY/2019' ) ) FROM DUAL;
D) SELECT TO_CHAR (SYSDATE, ' DD-MON-YYYY') - '01-JAN-2019' FROM DUAL;
E) SELECT ROUND (SYSDATE- '01-JAN-2019') FROM DUAL:
Answer：AC
(解析：在进行日期计算的时候需要用转换函数把字符型的转换成日期型，oracle 不会隐式转换。)
