Re: HELP why will the statement update all the order_date to Sysdate?

"OracleDream" <fateuk.w_at_googlemail.com> schreef in bericht news:7efaef15-7bd3-448a-9489-3beea277c7a6_at_e39g2000hsf.googlegroups.com...
>I am preparing for 1z0--047 now. There is one question I can not
> understand.
>
>
> View the Exhibit and examine the structure of the ORDERS and
> ORDER_ITEMS tables.
>
> Orders
>
> NAME NULL? TYPE
> order_id not null number(12)
> order_date date
> customer_id number(6)
> order_total number(8,2)
>
>
> Order_Items
>
> NAME NULL? TYPE
> order_id not null number(3)
> product_id not null number(2)
> qty number(6,2)
> unit_price number(8,2)
>
>
> In the ORDERS table, ORDER_ID is the PRIMARY KEY and ORDER_DATE has
> the DEFAULT value as SYSDATE.
>
> Evaluate teh following statement:
>
> UPDATE orders
> SET order_date=DEFAULT
> WHERE order_id IN (SELECT order_id FROM order_items
> WHERE qty IS NULL);
>
>
> What would be the outcome of the above statement?
>
> A. The UPDATE statement would not work because the main query and the
> subquery use different tables.
> B. The UPDATE statement would not work because the DEFAULT value can
> be used only in INSERT statements.
> C. The UPDATE statement would change all ORDER_DATE values to SYSDATE
> provided the current
> ORDER_DATE is NOT NULL and QTY is NULL.
> D. The UPDATE statement would change all the ORDER_DATE values to
> SYSDATE irrespective of what the
> current ORDER_DATE value is for all orders where QTY is NULL.
>
> The answer is D. I don't get it. I tested this statement serveral
> times. the answer should be C ( at least C is the closest question)
>
>
> Please help, guys!

Did you notice the NOT in

>provided the current ORDER_DATE is NOT NULL

?

With the DEFAULT clause, null values will be updated too, so C could NEVER be correct. I tested this on my db and D is correct: ALL records will be updated to sysdate.

Shakespeare Received on Wed Jun 25 2008 - 01:54:53 CDT