if exists (select * from dbo.sysobjects where id 
= object_id(N'[dbo].[Таблица1]') and OBJECTPROPERTY(id, N'IsUserTable') =  1 )
drop table [dbo].[Таблица1]
GO

CREATE TABLE [dbo].[Таблица1] (
	[Dt] [int] NOT NULL ,
	[Kod] [int] NOT NULL ,
	[Sum1] [money] NOT NULL ,
	[Sum2] [money] NOT NULL 
) ON [PRIMARY]
GO

ALTER TABLE [dbo].[Таблица1] WITH NOCHECK ADD 
	CONSTRAINT [DF_Таблица1_Sum1] DEFAULT ( 0 ) FOR [Sum1],
	CONSTRAINT [DF_Таблица1_Sum2] DEFAULT ( 0 ) FOR [Sum2],
	CONSTRAINT [PK_Таблица1] PRIMARY KEY  CLUSTERED 
	(
		[Dt],
		[Kod]
	)  ON [PRIMARY] 
GO
set nocount on
declare @iMax int, @i int
select @iMax =  100000 , @i =  1 
WHILE @i<@iMax
BEGIN
	INSERT INTO [Таблица1](Dt, Kod, Sum1, Sum2)
	VALUES(@i,convert(int, RAND()* 100 ), 1 , 2 )
	set @i=@i+ 1 
END

UPDATE t1 
SET t1.Sum1 = [t1].[Sum2] 
FROM Таблица1 t1
WHERE (t1.Dt) In (SELECT Min(t2.Dt) 
FROM Таблица1 t2 WHERE t2.Kod = t1.Kod)

UPDATE t1 
SET t1.Sum1 = [t1].[Sum2] 
FROM Таблица1 t1
WHERE (t1.Dt) = (SELECT Min(t2.Dt) 
FROM Таблица1 t2 WHERE t2.Kod = t1.Kod)

  | --Clustered Index Update(OBJECT:([Northwind].[dbo].[Таблица1].[PK_Таблица1]), SET:([Таблица1].[Sum1]=[t1].[Sum2]))
 
       | --Table Spool
 
            | --Top(ROWCOUNT est 0)
 
                 | --Nested Loops(Inner Join, OUTER REFERENCES:([t2].[Kod], [Expr1002]) WITH PREFETCH)
 
                      | --Hash Match(Aggregate, HASH:([t2].[Kod]) DEFINE:([Expr1002]=MIN([t2].[Dt])))
 
                      |    | --Clustered Index Scan(OBJECT:([Northwind].[dbo].[Таблица1].[PK_Таблица1] AS [t2]))
 
                      | --Clustered Index Seek(OBJECT:([Northwind].[dbo].[Таблица1].[PK_Таблица1] AS [t1]), SEEK:([t1].[Dt]=[Expr1002] AND [t1].[Kod]=[t2].[Kod]) ORDERED FORWARD)