几小时的DateDIFF，TIMESTAMPDIFF

Question

For the hours I use it as date data type. When I subtract it, it just normally deducts. How can I subtract it in time format like hours? I tried put datediff , timestampdiff , but it says invalid identifier . Must I create any function before executing? Or did I not activate datediff on Oracle?

Below is my code:

Select S.Test_Date, E.Testno, S.Examno, S.Serialno, 'Science'
      ,DATEDIFF(hours, F.STARTED, F.ENDED) as hours From Semester S, TIME F
      ,TESTPAPERS e
Where S.Testno= F.Testno
And E.Testno =1;

For timestampdiff:

Insert Into Test (Test_Date, Testno, Examno, Serialno, Type, Hours)
Select S.Test_Date, E.Testno, S.Examno, S.Serialno, 'Science'
     , TIMESTAMPDIFF(F.STARTED- F.ENDED) as hours From Semester S, TIME F
     , TESTPAPERS e
Where S.Testno= F.Testno
And E.Testno =1;

Answer 1

In Oracle, you can do arithmetic on date/time expressions easily. Subtracting one expression from another yields the number of days (with floating-point precision) between the two expressions.

For example, sysdate is right now, sysdate-1 is exactly one day ago, sysdate-(1/24) is one hour ago, and so forth.

So if you have two date/time items named when and then , the number of hours between them is (when-then)*24

No need to make it more complex than that if you're staying in Oracle. You don't need datediff, which is good because it isn't there.