Update table with using NEWID() function

CREATE TABLE Products(Id INT, Name CHAR(100), DefaultImageId INT NULL);

INSERT INTO Products (Id, Name, DefaultImageId) VALUES(1, 'A', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(2, 'A', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(3, 'A', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(4, 'A', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(5, 'A', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(1, 'B', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(2, 'B', NULL);
INSERT INTO Products (Id, Name, DefaultImageId) VALUES(3, 'B', NULL);

In general, I would update a table randomly like the following scripts.

update a
    set DefaultImageId=1
from Products as a
where name = 'A' 
and id in (
    select top 2 id
    from Products as b
    where a.name = b.name
    order by newid()
)

However, I get some issue. It would update more/less then 2 rows. I try execute the following scripts many times for debug. The results are not always only two records. If I remove the order by newid(), the number of output result will be fine. It seems like the problem in newid(). How can I solve this problem? Thanks

select * 
from Products as a
where name = 'A' 
and id in (
    select top 2 id
    from Products as b
    where a.name = b.name
    order by newid()
)

Answer

You can try this:

UPDATE U SET DefaultImageId = 1
FROM(
      SELECT TOP 2 * FROM dbo.Products WHERE Name = 'A' ORDER BY NEWID()
) AS U

However if you filter out the DefaultImageId=1 in inner query, it would be even better too. You should note that in this case, the inner query might produce less than 2 records.

UPDATE U SET DefaultImageId = 1
FROM(
      SELECT TOP 2 * FROM dbo.Products WHERE Name = 'A' AND DefaultImageId <> 1 ORDER BY NEWID()
) AS U