SQL Server 2012

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--TestData
declare @table table (groupname varchar(50),
                      credit numeric(18,2),
                      debit numeric(18,2),
                      drcreffect varchar(50),
                      undergroup varchar(50)
                     )

declare @table1 table (groupname varchar(50),
                       credit numeric(18,2),
                       debit numeric(18,2),
                       drcreffect varchar(50),
                       undergroup varchar(50)
                      )

insert into @table 
values 
       ('Opening Stock',   200.00, 0.00, 'Dr', 'Opening Stock'),
       ('Opening Stock',   500.00, 0.00, 'Dr', 'Opening Stock'),
       ('Purchase',        0.00, 7500.00, 'Dr', 'Purchase'),
       ('Purchase Return', 7000.00, 0.00, 'Dr', 'Purchase'),
       ('Purchase Return', 200.00, 0.00, 'Dr', 'Purchase');

SELECT 
		RN = ROW_NUMBER() OVER(ORDER BY groupname),
		undergroup,
		groupname,
		credit+debit Amt,
		LAG(debit, 1,0) OVER(PARTITION BY undergroup ORDER BY undergroup)+credit AS Total
	FROM
	(
		SELECT DISTINCT
			groupname,
			SUM(credit) OVER(PARTITION BY groupname) AS Credit,
			SUM(debit*-1) OVER(PARTITION BY groupname) AS debit,
			undergroup
		FROM @table
	)X;

--Query
with CTE as (
	SELECT 
		RN = ROW_NUMBER() OVER(ORDER BY groupname),
		undergroup,
		groupname,
		credit+debit Amt,
		LAG(debit, 1,0) OVER(PARTITION BY undergroup ORDER BY undergroup)+credit AS Total
	FROM
	(
		SELECT DISTINCT
			groupname,
			SUM(credit) OVER(PARTITION BY groupname) AS Credit,
			SUM(debit*-1) OVER(PARTITION BY groupname) AS debit,
			undergroup
		FROM @table
	)X
)
select 
	RN,
	undergroup,
	groupname,
	case when Amt < 0 then -1*Amt else Amt end as Amt,
	case when Total < 0 then -1*Total else Total end as Total
from CTE

RN	undergroup	groupname	Amt	Total
1	Opening Stock	Opening Stock	700.00	700.00
2	Purchase	Purchase	-7500.00	0.00
3	Purchase	Purchase Return	7200.00	-300.00

RN	undergroup	groupname	Amt	Total
1	Opening Stock	Opening Stock	700.00	700.00
2	Purchase	Purchase	7500.00	0.00
3	Purchase	Purchase Return	7200.00	300.00