在 SQL Server 中计算运行总计

Update，如果您运行的是SQL Server 2012，请参阅:https://stackoverflow.com/a/10309947

问题是Over子句的SQL Server实现是somewhat limited.

Oracle(和ANSI-SQL)允许您执行以下操作:

 SELECT somedate, somevalue,
  SUM(somevalue) OVER(ORDER BY somedate 
     ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) 
          AS RunningTotal
  FROM Table

SQL Server并没有为这个问题提供干净的解决方案.我的直觉告诉我，这是光标最快的罕见 case 之一，尽管我必须对重大结果进行一些基准测试.

更新技巧很方便，但我觉得它相当脆弱.如果您正在更新一个完整的表，那么它将按照主键的顺序进行.所以，如果你把日期设为主键，你就安全了.但您依赖的是一个未记录的SQL Server实现细节(如果查询最终由两个过程执行，我想知道会发生什么，请参阅:MAXDOP):

完整工作样本:

drop table #t 
create table #t ( ord int primary key, total int, running_total int)

insert #t(ord,total)  values (2,20)
-- notice the malicious re-ordering 
insert #t(ord,total) values (1,10)
insert #t(ord,total)  values (3,10)
insert #t(ord,total)  values (4,1)

declare @total int 
set @total = 0
update #t set running_total = @total, @total = @total + total 

select * from #t
order by ord 

ord         total       running_total
----------- ----------- -------------
1           10          10
2           20          30
3           10          40
4           1           41

你要求提供一个基准，这是事实真相.

最快的安全方法是使用光标，它比交叉连接的相关子查询快一个数量级.

最快的方法就是更新技巧.我唯一担心的是，我不确定在所有情况下，更新都会以线性方式进行.查询中没有明确说明这一点.

总之，对于生产代码，我将使用光标.

测试数据:

create table #t ( ord int primary key, total int, running_total int)

set nocount on 
declare @i int
set @i = 0 
begin tran
while @i < 10000
begin
   insert #t (ord, total) values (@i,  rand() * 100) 
    set @i = @i +1
end
commit

测试1:

SELECT ord,total, 
    (SELECT SUM(total) 
        FROM #t b 
        WHERE b.ord <= a.ord) AS b 
FROM #t a

-- CPU 11731, Reads 154934, Duration 11135 

测试2:

SELECT a.ord, a.total, SUM(b.total) AS RunningTotal 
FROM #t a CROSS JOIN #t b 
WHERE (b.ord <= a.ord) 
GROUP BY a.ord,a.total 
ORDER BY a.ord

-- CPU 16053, Reads 154935, Duration 4647

测试3:

DECLARE @TotalTable table(ord int primary key, total int, running_total int)

DECLARE forward_cursor CURSOR FAST_FORWARD 
FOR 
SELECT ord, total
FROM #t 
ORDER BY ord


OPEN forward_cursor 

DECLARE @running_total int, 
    @ord int, 
    @total int
SET @running_total = 0

FETCH NEXT FROM forward_cursor INTO @ord, @total 
WHILE (@@FETCH_STATUS = 0)
BEGIN
     SET @running_total = @running_total + @total
     INSERT @TotalTable VALUES(@ord, @total, @running_total)
     FETCH NEXT FROM forward_cursor INTO @ord, @total 
END

CLOSE forward_cursor
DEALLOCATE forward_cursor

SELECT * FROM @TotalTable

-- CPU 359, Reads 30392, Duration 496

测试4:

declare @total int 
set @total = 0
update #t set running_total = @total, @total = @total + total 

select * from #t

-- CPU 0, Reads 58, Duration 139