DECLARE Purch CURSOR FOR 
	  SELECT DISTINCT(Partner) FROM  Table_Purch WHERE Partner IS NOT NULL 
	  OPEN Purch
	  FETCH NEXT FROM Purch   
	  INTO @Partnr  
  
	 	WHILE @@FETCH_STATUS = 0  
		BEGIN  
			SET @i = (SELECT NumRow FROM TblRowPartSum WHERE Partner = @Partnr)
			UPDATE Table_Purch 
		SET Table_Purch .Sum = upd.SummCorr
		FROM Table_Purch  	
		LEFT JOIN TblRowPartSum upd ON upd.Partner = Table_Purch.PARTNER 
		WHERE Partner = @Partnr
		ORDER BY DatePay OFFSET (@i+1) ROWS FETCH NEXT 1 ROWS ONLY
	
			FETCH NEXT FROM Purch INTO @Partnr
		END;
	  CLOSE Purch
	  DEALLOCATE Purch