SQL running totals and subtractions

[sterjo]

I have a table for which I need a “special” running total. More specifically there should be a close communication between the credit and the debit column. The scenario should be in the following order

“Credit”	“Debit”	“Balance credit”	“Balance debit”
6	   0	    6	                     0
5	   0	   11                            0
0	   4	    7                            0
0	   9	    0                            2
3	   0	    1	                     0
0	   5	    0	                     4
0	   2	    0	                     6

I have to point out that this is done in a grouped form, where the CustormerID is the grouped clause. Now I have achieved this to a point where the calculations work only if the credit column is bigger than 0, but when the account starts with debit I get only sums of the column not the needed subtractions.
What am I missing? Thanks in advance.

DECLARE @PrevRunBal MONEY --Overall running total    
SET @PrevRunBal = 0
DECLARE @PrevGrpBal MONEY --Running total resets when account changes SET @PrevGrpBal = 0
DECLARE @PrevRunCnt INT   --Overall running count (ordinal rank)  
SET @PrevRunCnt = 0
DECLARE @PrevGrpCnt INT   --Running count resets when account changes  
SET @PrevGrpCnt = 0
DECLARE @PrevAcctID INT   --The "anchor" and "account change detector" SET @PrevAcctID = 0
changes 
SET @PrevGrpBalP = 0
      

 update Temp
        
        SET --===== Running Total      
        @PrevRunBal  = RunBal = @PrevRunBal + dolguva,
        --  @iznos =RunBal= dolguva - pobaruva + @sdol -@spob,
        --===== Grouped Running Total (Reset when account changes)   
            @PrevGrpBal  = Bcredit = CASE  
                                        
                   WHEN CustomerID = @PrevAcctID  
                         THEN CASE
                         WHEN CREDIt > DEBIT or CREDIT = 0
                         THEN (@PrevGrpBal+CREDIT)-(DEBIT)
                         WHEN  DEBIT>CREDIT or DEBIT =0
                         THEN (@PrevGrpBal+DEBIT)-DEBIt
                         END
                   ELSE CASE         
                        WHEN CREDIT >DEBIT 
                        THEN (CREDIT)   
                        WHEN DEBIT > CREDIT
                        THEN DEBIT    -- restarts from 0 if only 1 rec.
                        END             
                             
                  END,
                     
      
        --===== Running Count (Ordinal Rank)      
          @PrevRunCnt  = RunCnt = @PrevRunCnt + 1,
 --===== Grouped Running Total (Ordinal Rank, Reset when account changes)   
             @PrevGrpCnt  = GrpCnt = CASE   
                                     WHEN CustomerID = @PrevAcctID    
                                     THEN @PrevGrpCnt + 1          
                                     ELSE 1 -- Restarts count at "1"     
                                     END,

 --===== "Anchor" and provides for "account change detection"   
             @PrevAcctID = CustomerID