SQL Join only on condition?

I have开发者_运维问答 about 10 different sql statements that update different tables. They look similar to this:

Update Y 
SET x = n
Where something = @somevar

Now I need to Update only certain rows when the @hasRows var is set. I could simply do this:

if not @hasRows is null
begin
    Update Y     
    SET x = n
    from Y inner join #items on y.Item = #items.Item
    Where something = @somevar
end
else
begin
    Update Y 
    SET x = n
    Where something = @somevar
end

Is there a way to avoid the if/else and do the update in one statement?

I am using SQL2005.

Perhaps something like this: (copypasta your example)

UPDATE Y     
SET x = n
FROM Y 
WHERE something = @somevar
AND (
    (@Items IS NULL)
    OR (y.Item = @Item)
    )

The JOIN isn't used but it's always proceeding if @items is NULL, or using the intended condition.

Problem here is that your example seems to include a TVP @ITEMS but TVPs don't exist in SQLServer2k5? So whatever the value is should be placed in the parameter.

Alternatively, if #Table exists but has no rows you can do this:

UPDATE Y     
SET x = n
FROM Y 
JOIN #Items ON (@HasRows = 0) OR (#Items.Item = Y.Item)
WHERE something = @somevar

If you don't know whether or not #Items IS NULL then your condition is your option because declared variables are resolved before the statement is executed.