How to UPDATE TOP 400?
UPDATE db.dbo.tbl SET column1 = 2 WHERE primaryID IN ( SELECT TOP (400) primarkyID FROM db.dbo.tbl WHERE column2 = 1 AND column1 IS NULL )But I don't like this as there's no way to guarantee WHICH top 400, you might want to add some other type of criteria. And even an Order By to the subquery.
WITH q AS ( SELECT TOP 400 * FROM db.dbo.tb WHERE column2 = 1 AND column1 is null ORDER BY column3 -- choose your order! )UPDATE qSET column2 = 2
How would you determine the top 400? With no order by there is no guanantee that the same set would always be selected and thus the wrong records could be updated.