Best way to update 40 million rows in batch

Question

Basically I need to run this on a table with 40 million rows, updating every row at once will crash, so I want to batch the query so that if it crash, it can re-run the quer

Answer 1

Select 1;  -- this will set a rowcount
WHILE (@@Rowcount > 0)   
BEGIN
  UPDATE TOP (1000000) [table]   
    SET [New_ID] =  [Old_ID]
  WHERE [New_ID] <> [Old_ID] 
    or ([New_ID] is null and [Old_ID] is not null)
END

100000 may work better for the top.

Since NewID and OldID is not null then the is null check is not necessary.