Question

Suppose I have a SQL table of Awards, with fields for Date and Amount. I need to generate a table with a sequence of consecutive dates, the amount awarded in each day, and the running (cumulative) total.

Date         Amount_Total   Amount_RunningTotal
----------   ------------   -------------------
1/1/2010              100                   100
1/2/2010              300                   400
1/3/2010                0                   400
1/4/2010                0                   400
1/5/2010              400                   800
1/6/2010              100                   900
1/7/2010              500                  1400
1/8/2010              300                  1700

This SQL works, but isn’t as quick as I’d like:

Declare @StartDate datetime, @EndDate datetime 
Select @StartDate=Min(Date), @EndDate=Max(Date) from Awards 

; With 

/* Returns consecutive from numbers 1 through the 
number of days for which we have data */
Nbrs(n) as (
   Select 1 Union All 
   Select 1+n 
   From Nbrs 
   Where n<=DateDiff(d,@StartDate,@EndDate)),

/* Returns all dates @StartDate to @EndDate */
AllDays as (
   Select Date=DateAdd(d, n, @StartDate) 
   From Nbrs ) 

/* Returns totals for each day */
Select 
 d.Date,
 Amount_Total = (
        Select Sum(a.Amount) 
        From Awards a 
        Where a.Date=d.Date),
 Amount_RunningTotal = (
        Select Sum(a.Amount) 
        From Awards a 
        Where a.Date<=d.Date)
From AllDays d
Order by d.Date 
Option(MAXRECURSION 1000)

I tried adding an index to Awards.Date, but it made a very minimal difference.

Before I resort to other strategies like caching, is there a more efficient way to code the running total calculation?

Answer 1

I generally use a temporary table for this:

DECLARE @Temp TABLE
(
    [Date] date PRIMARY KEY,
    Amount int NOT NULL,
    RunningTotal int NULL
)

INSERT @Temp ([Date], Amount)
    SELECT [Date], Amount
    FROM ...

DECLARE @RunningTotal int

UPDATE @Temp
SET @RunningTotal = RunningTotal = @RunningTotal + Amount

SELECT * FROM @Temp

If you can’t make the date column a primary key then you need to include an ORDER BY [Date] in the INSERT statement.

Also, this question’s been asked a few times before. See here or search for “sql running total”. The solution I posted is, as far as I know, still the one with the best performance, and also easy to write.