Case 로 할 필요없이

Inline View 로 Join 하는게 효율적으로 보입니다.

1. 원데이터 Select

2. 계약기간 이전데이터 Inline View 로 가져옴

3. 계약기간 이후데이터 Inline View 로 가져옴

1의 데이터에 2,3 의 데이터를 Join

하기 쿼리 참고하세요..

---쿼리시작---

Declare @ls_from_ymd char(8) = '2015-05-01'
Declare @ls_to_ymd   char(8) = '2016-04-30'

Declare @ls_from_yymm char(7) = Left(@ls_from_ymd,7)
Declare @ls_to_yymm   char(7) = Left(@ls_to_ymd  ,7)

;with tblA (month,amt) As
(
     Select '2015-04', 1500000  Union All
     Select '2015-05', 500000   Union All
     Select '2015-06', 500000   Union All
     Select '2015-07', 1500000  Union All
     Select '2015-08', 500000   Union All
     Select '2015-09', 500000   Union All
     Select '2015-10', 500000   Union All
     Select '2015-11', 500000   Union All
     Select '2015-12', 500000   Union All
     Select '2016-01', 500000   Union All
     Select '2016-02', 500000   Union All
     Select '2016-03', 500000   Union All
     Select '2016-04', 500000   Union All
     Select '2016-05', 2500000  Union All
     Select '2016-06', 3500000
)    

     Select a.month
           ,SUM(a.amt) + ISNULL(Max(b.amt),0) + ISNULL(Max(c.amt),0) 
       From tblA a
                   --계약기간 이전 데이터
                   Left Outer Join
                                   (
                                       Select @ls_from_yymm As month
                                             ,SUM(a.amt)   As amt
                                         From tblA a
                                        Where a.month < @ls_from_yymm
                                   ) b 
                                       On a.month = b.month                                            
                   --계약기간 이후 데이터
                   Left Outer Join
                                   (
                                       Select @ls_to_yymm As month
                                             ,SUM(a.amt)   As amt
                                         From tblA a
                                        Where a.month > @ls_to_yymm
                                   ) c 
                                       On a.month = c.month                                            
      Where a.month Between @ls_from_yymm And @ls_to_yymm                                      
   Group By a.month 
   ---쿼리끝---

본문글에 작성해두신 쿼리 토대로 조금 수정해봤습니다..

그럼 수고하세요~

Declare @ls_from_ymd char(8) = '2015-05-01'
Declare @ls_to_ymd   char(8) = '2016-04-30'

;with tblA(cType,so_code,ma_p_code,sContractDate,eContractDate,ma_date,money) As
(
          Select a.cType
                ,a.so_code
                ,a.ma_p_code
                ,a.sContractDate
                ,a.eContractDate
                ,b.ma_date
                ,b.money
            From view_so_detail a
                                  Inner Join
                                             MaMcDetail b
                                                          On a.so_code = b.so_code
                                                         And a.ma_p_code = b.ma_p_code
                                                         And b.use_yn = 1
           Where a.use_yn = 1
)
          Select a.cType
                ,a.so_code
                ,Sum(Convert(money,a.money)) + IsNull(Max(Convert(money,b.money)),0) + IsNull(Max(Convert(money,c.money)),0) As cost
                ,Left(a.ma_date,7) As ma_date
            From tblA a
                        Left Outer Join
                                        (
                                             Select a.cType
                                                   ,a.so_code
                                                   ,Sum(Convert(money,a.money)) As money
                                                   ,@ls_from_ymd As ma_date
                                               From tblA a
                                              Where a.ma_date < @ls_from_ymd   
                                        ) b
                                            On a.cType = b.cType
                                           And a.so_coe = b.so_code
                                           And a.ma_date = b.ma_date
                        Left Outer Join
                                        (
                                             Select a.cType
                                                   ,a.so_code
                                                   ,Sum(Convert(money,a.money)) As money
                                                   ,@ls_to_ymd As ma_date
                                               From tblA a
                                              Where a.ma_date > @ls_to_ymd   
                                        ) b
                                            On a.cType = c.cType
                                           And a.so_coe = c.so_code
                                           And a.ma_date = c.ma_date
           Where a.ma_date Between @ls_from_ymd And @ls_to_ymd
        Group By a.cType
                ,a.so_code
                ,Left(a.ma_date,7)