Why does this cause an ArithmeticException in C# when SQLPlus is all ok

Question

I have a view connecting 4 tables

CREATE VIEW BookCopyInfo 
AS
SELECT
  bc.BookCopyID, b.BookTitle, m.FirstName || ' ' || m.LastName AS BorrowedBy,
  l.expectedReturnDate, (SYSDATE - l.expectedReturnDate) AS NoOfDaysLate
FROM Book b, Member m, Lending l, BookCopy bc
WHERE b.BookID = bc.BookID AND l.MemberID = m.MemberID
  AND l.BookCopyID = bc.BookCopyID

There is a small date arithmetic going on that finds how many days was a book late

(SYSDATE - l.expectedReturnDate)

When i do a SELECT * FROM BookCopyInfo, i get rows like

4  | Human Computer Interaction | Alan Paul | 10-JUL-10  | -13.642292

So it is correct and -13 is the correct answer actually.

DESC BookCopyInfo returns

 Name                                      Null?    Type
 ----------------------------------------- -------- ---------------

 BOOKCOPYID                                NOT NULL NUMBER(38)
 BOOKTITLE                                 NOT NULL VARCHAR2(100)
 BORROWEDBY                                         VARCHAR2(126)
 EXPECTEDRETURNDATE                        NOT NULL DATE
 NOOFDAYSLATE                                       NUMBER(38)

However in C#

DataTable dtBookInfo = new DataTable();
da = new OracleDataAdapter("SELECT * FROM BookCopyInfo", con);
da.Fill(dtBookInfo);

catches an exception in the da.Fill line

OverflowException was unhandled by user code.
Arithmetic operation resulted in an overflow.

Why does it work fine in SQLPlus but fails in C#? :S

Answer 1

I believe it has to with SQL-Number data type. You can try the following option..

1) .... Round((SYSDATE - l.expectedReturnDate),2 ) ...

2) Convert the data type of "NoOfDaysLate" to integer.

Answer 2

IF you are just interested in some part of the difference between the two dates, then you should use DateDiff instead...

Eg: DATEDIFF(yy, startDate, endDate) YearsPassedSinceStart

returns the no. of years passed since the start date.

Similarly to find number of months, use 'm' as the datepart or 'd' to determine no. of days.