Update Statement With Decode and Business Dates

Question

Hello everyone,
I need to write a UPDATE statement using business date rule. In general, the due date is 30 days from the checkout date. If the due date falls on a Saturday or Sunday then the loan period is 32 days.
I know that to test for a weekday, I'd need to use the to_char function in Oracle with the format of ‘D’. I did some research and found that to test which weekday November 12, 2007 falls on, I'd need to use the expression to_char(’12-NOV-2007’,’D’). This function returns a number between 1 and 7. 1 represents Sunday, 2 Monday, …,7 Saturday.
What I really would need to do is write one UPDATE statement using an expression with the Decode function and the to_Char function:
UPDATE book_trans SET due_dte = expression
These are the transactions that will need to be updated:
ISBN 0-07-225790-3 checked out on 15-NOV-2007 by employee 101(book_trans_id=1)
ISBN 0-07-225790-3 checked out on 12-NOV-2007 by employee 151(book_trans_id=2)
ISBN 0-201-69471-9 checked out on 14-NOV-2007 by employee 175(book_trans_id=3)
ISBN 0-12-369379-9 checked out on 16-NOV-2007 by employee 201(book_trans_id=4)
I manually calculated the due-dte and wrote update statement for each book_trans_id:
UPDATE book_trans SET due_dte = '17-dec-07' WHERE book_trans_id = 1;
UPDATE book_trans SET due_dte = '12-dec-07' WHERE book_trans_id = 2;
UPDATE book_trans SET due_dte = '14-dec-07' WHERE book_trans_id = 3;
UPDATE book_trans SET due_dte = '18-dec-07' WHERE book_trans_id = 4;
As you can see, it's very cumbersome and I'd just like to know how to incorporate everything in one Update statement:
UPDATE book_trans SET due_dte = expression
so that if due date falls on Saturday or Sunday, the loan period is 32 days; weekday, loan period is 30 days.
Any tips or help will be greatly appreciated. Thanks!

Answer 1

Hi,
882300 wrote:
Hello everyone,
I need to write a UPDATE statement using business date rule. In general, the due date is 30 days from the checkout date. If the due date falls on a Saturday or Sunday then the loan period is 32 days. That's equivalent to saying that the due date is normally 30 days after the checkout date, but if the checkout date falls on a Thursday or Friday, then the due date is 32 days after the checkout date. I used this equivalent in the statement below.
I know that to test for a weekday, I'd need to use the to_char function in Oracle with the format of ‘D’. I did some research and found that to test which weekday November 12, 2007 falls on, I'd need to use the expression to_char(’12-NOV-2007’,’D’). This function returns a number between 1 and 7. 1 represents Sunday, 2 Monday, …,7 Saturday.That's just one way to find out the weekday, and it's error-prone because it depends on your NLS_TERRITORY setting. A more reliable way is to use 'DY' or 'DAY' as the 2nd argument to TO_CHAR. That depends on NLS_DATE_LANGUAGE, but you can explicitly set the language in the optional 3rd argument to TO_CHAR, which means your code will work the same no matter what the NLS settings happen to be. It's also easier to debug: you may have to think whether '1' means Sunday or Monday, but it's easy to remember that 'SUN' means Sunday.
What I really would need to do is write one UPDATE statement using an expression with the Decode function and the to_Char function:
UPDATE book_trans SET due_dte = expressionHere's one way:
UPDATE  book_trans
SET     due_dte = checkout_dte + CASE
                                  WHEN  TO_CHAR ( checkout_dte
                                         , 'fmDAY'
                                 , 'NLS_DATE_LANGUAGE=ENGLISH'
                                 ) IN ('THURSDAY', 'FRIDAY')
                         THEN  32
                         ELSE  30
                              END
WHERE   book_trans_id      IN (1, 2, 3, 4)
;This assumes that checkout date is a column in the same table.