Update with the expression:
UPDATE [dbo].[SampleTable] SET [Col1] = @a + @b + @c
Update using the .WRITE() clause:
UPDATE [dbo].[SampleTable] SET [Col1].WRITE('New Value, 0, NULL)
UPDATE [dbo].[SampleTable] SET [Col1].WRITE(@a + @b + @c, 0, NULL)
UPDATE [dbo].[SampleTable] SET [Col1].WRITE(@x, 500, 1000)