update [SalesToList]
  set  
    [SalesToList].[Count]=[SalesToList].[Count]+
       (select
          [Count] 
        from 
          [Sales] 
        where 
          [SaleID]= 1  and 
          [ID]=[SalesToList].[ID] and 
          [PGroup]=[SalesToList].[PGroup] and 
          [Shop]=[SalesToList].[Shop] and 
          [Price]=[SalesToList].[Price]
       )
  where 
    exists 
      (select 
         * 
       from 
         [Sales] 
       where  
         [SaleID]= 1  and 
         [ID]=[SalesToList].[ID] and 
         [PGroup]=[SalesToList].[PGroup] and 
         [Shop]=[SalesToList].[Shop] and 
         [Price]=[SalesToList].[Price]
      )

create table [Sales] 
(
  [SaleID] INT NOT NULL, 
  [ID] INT NOT NULL, 
  [PGroup] INT NOT NULL, 
  [Shop] INT NOT NULL, 
  [Count] INT NOT NULL, 
  [Price] FLOAT NOT NULL, 
  [Date] DATETIME, 
  [Time] DATETIME NOT NULL
)

create table [SalesToList] 
(
  [ID] INT NOT NULL, 
  [PGroup] INT NOT NULL, 
  [Shop] INT NOT NULL, 
  [Count] INT NOT NULL, 
  [Price] FLOAT
)

insert into Sales ([ID], [PGroup], [Shop], [Count], [Price]) values ( 1 ,  11 ,  1 ,  1 ,  10 )
insert into Sales ([ID], [PGroup], [Shop], [Count], [Price]) values ( 2 ,  11 ,  1 ,  2 ,  10 )
insert into Sales ([ID], [PGroup], [Shop], [Count], [Price]) values ( 3 ,  11 ,  1 ,  3 ,  10 )
insert into SalesToList ([ID], [PGroup], [Shop], [Count], [Price]) values ( 1 ,  11 ,  1 ,  5 ,  10 )
insert into SalesToList ([ID], [PGroup], [Shop], [Count], [Price]) values ( 2 ,  11 ,  1 ,  10 ,  10 )

insert into Sales ([SaleID], [ID], [PGroup], [Shop], [Count], [Price], [Time]) values ( 1 ,  1 ,  11 ,  1 ,  1 ,  10 ,  0 )
insert into Sales ([SaleID], [ID], [PGroup], [Shop], [Count], [Price], [Time]) values ( 1 ,  2 ,  11 ,  1 ,  2 ,  10 ,  0 )
insert into Sales ([SaleID], [ID], [PGroup], [Shop], [Count], [Price], [Time]) values ( 1 ,  3 ,  11 ,  1 ,  3 ,  10 ,  0 )