フリー問題

問題文

A query needs the length of service of each employee. The developer writes SYSDATE - hire_date in the select list. What is the data type and the meaning of the value that this expression returns?

選択肢

1. A number that counts seconds, because subtracting one datetime value from another yields a number and the database reads such a number as a count of seconds.
2. An interval that counts days and seconds, because subtracting one datetime value from another yields a value of the interval data type in every case.
3. A date that marks the anniversary, because subtracting one datetime value from another yields a datetime value and the database reads it as a point in time.
4. A number that counts days, because subtracting one datetime value from another yields a number and the database reads such a number as a count of days.