update value only when changed - asp.net

Question

I had a good look around but couldn't quite find the answer to this one:
I got a Stored Procedure that updates around 30 Fields on a SQL SERVER 2008 Table. It's important for me that one of those Fields is only getting updated, if the value actually changed.
The Stored Procedure Snippet at the moment:
ALTER PROCEDURE test
#p_RoomNo int,
[RoomNo] = #p_RoomNo,
I tried changing it for that particular Column to COALESCE / ISNULL in the SET-Clause of the Procedure, but it still Updates that Column as well
[RoomNo] = COALESCE(#p_RoomNo,RoomNo),
[RoomNo] = ISNULL(#p_RoomNo,RoomNo),
both give me the same Output ...
Do you have any ideas how to NOT Update the Value on Server Side or do I have to put this on a .asp-Forum to change the Application to not pass on any values that are unchanged?
Thanks for any input!

Answer 1

I think the most proper place to check whether the values changed prior to storing the new value is in the asp side of the solution, not in the database. And then you can pass a parameter to the stored procedure.
In the procedure, base on that parameter, you decide whether you should change the value or not.
Edit: Suppose you have a server control of the HiddenField type.
Page_Load(object sender, EventArgs e) {
if (IsPostBack) {
if (myTextBoxIWannaCheckForChanges.Text != myHiddenField.Value) {
// The value has changed.
}
}
}
Note that this will check for changes during the page load. You could also use that kind of logic while handling a button click (if you do so, you don't have to check for a PostBack). Like this:
foo_clicked (object sender, EventArgs args) {
SqlCommand command = // ...snip
// ... set everything you need for your command.
bool changed = (myTextBoxIWannaCheckForChanges.Text != myHiddenField.Value);
command.Parameters.AddWithValue("#changed", changed);
// ... finally let the command execute.
}

Answer 2

Thanks for all replies ...
Changing the Front-End-Application was no option in the end, because changes wouldn't reflect in Future Versions seeing that it's 3rd Party.
I tried most options to alter the SProc but either ran into not getting the desired Field Value updated at all (even when the Value changed) or updating all the times. I decided to look more into the problem from the other side (why I wanted this field not to be updated when the Value didn't change, which was an Update-Trigger, that should only fire when the Value of that Field actually changed.
In the end, the solution was very simple:
Seeing that the
IF UPDATE (RoomNo)
in the Trigger doesn't really compare the Value of the Field but merely if there's an Update called, I simply had to add the comparison via INSERTED and DELETED, so I added the join with DELETED, set my Where Clause on it and it works :)
ALTER trigger [dbo].[UpdateDepartDate]
on [dbo].[Customer]
for update
As
Begin
if update (RoomNo)
Begin
UPDATE Customer
SET [DepartDate] = null
FROM Rooms r
INNER JOIN Customer cu
ON cu.[RoomNo] = r.[Room_ID]
Join INSERTED INS
ON cu.[CU_ID] = INS.[CU_ID]
join Deleted Del
ON INS.[CU_ID] = DEL.[CU_ID]
WHERE INS.[RoomNo] <> DEL.[RoomNo]
END
END
Thought I post it here for anyone interested :)
Thanks again everyone for your help