É fácil:
DECLARE @BatchSize INT
SET @BatchSize = 100000
WHILE @BatchSize <> 0
BEGIN
DELETE TOP (@BatchSize)
FROM [dbo].[UnknownTable]
SET @BatchSize = @@rowcount
END
DECLARE @BatchSize INT
SET @BatchSize = 100000
WHILE @BatchSize <> 0
BEGIN
DELETE TOP (@BatchSize)
FROM [dbo].[UnknownTable]
SET @BatchSize = @@rowcount
END