How to add and subtract value from previous rows based on condition

问题

I have a table with values

Slno Type     Amount        
 1    P         40           
 2    C         20           
 3    P         45           
 4    P         20           
 5    C         10

I want to get values for RESULT column.

   Type      Amount       RESULT 
    P         40           40
    C         20           20
    P         45           65
    P         20           85
    C         10           75

If Type is C then value gets subtracted from previous value, else if Type is P then value gets added to previous values.

This is what i've tried:

;WITH FINALMIDRESULT 
     AS (SELECT Type, 
                Value1, 
                Row_number() 
                  OVER( 
                    ORDER BY Slno ASC) rownum 
         FROM   #midRes) 
SELECT C1.Type, 
       C1.Value1, 
       CASE 
         WHEN C1.Type = 'C' THEN (SELECT Sum(Amount) 
                                  FROM   FINALMIDRESULT c2 
                                  WHERE  c2.rownum <= C1.rownum) 
         ELSE (SELECT Sum(Amount) - Sum(Amount) 
               FROM   FINALMIDRESULT c2 
               WHERE  c2.rownum <= C1.rownum) 
       END AS RESULT 
FROM   FINALMIDRESULT C1

This is the Result that i have got

  Type      Amount       RESULT 
    P         40           0
    C         20           60
    P         45           0
    P         20           0
    C         10           135

回答1:

You need to implement a seft INNER JOIN to sum all values with Slno less than the current value, like below:

;WITH   OriginalData    AS
(       SELECT  *
        FROM
        (       VALUES
                (1, 'P', 40),
                (2, 'C', 20),
                (3, 'P', 45),
                (4, 'P', 20),
                (5, 'C', 10)
        )       AS Temp(Slno, Type, Amount)
)
SELECT      [Current].Type, [Current].Amount,
            ISNULL(SUM(
            CASE    WHEN  [Previous].Type = 'P'
                    THEN +[Previous].Amount
                    ELSE -[Previous].Amount
            END),0) + 
            CASE    WHEN  [Current].Type = 'P'
                    THEN +[Current].Amount
                    ELSE -[Current].Amount
            END Result
 FROM       OriginalData [Current]
 LEFT JOIN  OriginalData [Previous]
        ON  [Previous].Slno < [Current].Slno
GROUP BY    [Current].Slno, [Current].Type, [Current].Amount
ORDER BY    [Current].Slno

I think the biggest change you can make is to shift your mindset. When you think "previous values" you chose a procedural path which can be solved my any major programming language, but rapidly evolve to a cursor approach in SQL -- what isn't appropriate in this case.

When comes to SQL, you need to think in "sets", so you can drive your efforts to identify those data sets and combine them.

回答2:

SELECT SlNo, Type, Amount, 
    Sum((Case when  Type='C' then -1 else 1 END)*Amount) Over(Order by SlNo)  Result
FROM TableName

来源：https://stackoverflow.com/questions/32066074/how-to-add-and-subtract-value-from-previous-rows-based-on-condition

标签

sql

sql-server-2008-r2