Update Top 1 Row In SQL Server I know that typically you would have an autonumber field - but in this instance there is not, and it honestly does not matter which row get's updated as long as it is only 1.

I have sample DDL like such one table that contains requested qty, and one table that contains avaliable qty.  I want to update @Test1.amtonhand with the value from @Test2.amtonhand and join on @Test1.nrs=@Test2.nrs but only update the 1 record in @Test1

How is this achieved in SQL Server 2008

    Declare @Test1 Table
(
    nrs varchar(100)
    ,amtrqst varchar(100)
    ,amtonhand varchar(100)
)

Declare @Test2 Table
(
    nrs varchar(100)
    ,amtonhand varchar(100)
)


Insert Into @Test1 (nrs, amtrqst) Values
('abc', '10'), ('abc', '12'), ('abc', '13'), ('def', '5'), ('def', '12')

Insert Into @Test2 (nrs, amtonhand) Values
('abc', '10'), ('def', '5')


EDIT
My desired results from the update would be

@Test1 --
abc, 10, 10
abc, 12
abc, 13
def, 5, 5
def, 12
If you don't care which row gets updated, you can use ROW_NUMBER with an arbitrary order:

WITH CTE AS
(
    SELECT  *,
            RN = ROW_NUMBER() OVER(PARTITION BY nrs ORDER BY (SELECT NULL))
    FROM @Test1
)
UPDATE a
SET a.amtonhand = b.amtonhand 
FROM CTE a
INNER JOIN @Test2 b
    ON a.nrs = b.nrs
WHERE a.RN = 1;


The results are:

╔═════╦═════════╦═══════════╗
║ nrs ║ amtrqst ║ amtonhand ║
╠═════╬═════════╬═══════════╣
║ abc ║      10 ║ 10        ║
║ abc ║      12 ║ NULL      ║
║ abc ║      13 ║ NULL      ║
║ def ║       5 ║ 5         ║
║ def ║      12 ║ NULL      ║
╚═════╩═════════╩═══════════╝