Sql server 什么更快：求和大于零还是大于0？

我有这样一个问题：

select sum(case when col1=@arg1 then value else null end) from t

就性能而言，使用

0

而不是

NULL

是否存在差异？像这样：

select sum(case when col1=@arg1 then value else 0 end) from t

结果:

Table 'sysschobjs'. Scan count 1, logical reads 1556, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 7 ms.

Table 'sysschobjs'. Scan count 1, logical reads 1556, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 6 ms.

Table 'sysschobjs'. Scan count 1, logical reads 1556, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.
 SQL Server Execution Times:
   CPU time = 0 ms,  elapsed time = 7 ms.

---

所以。。。答案-类似（如果我们只讨论性能）

在下面的测试中，我一致发现

NULL

稍微快一点

   SET STATISTICS TIME ON;
   DECLARE @i int = null; /*Or set to zero*/

   WITH 
    E1(N) AS 
    (
        SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
        SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL 
        SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1 UNION ALL SELECT 1
    )                                       -- 1*10^1 or 10 rows
    , E2(N) AS (SELECT 1 FROM E1 a, E1 b)   -- 1*10^2 or 100 rows
    , E4(N) AS (SELECT 1 FROM E2 a, E2 b)   -- 1*10^4 or 10,000 rows
    , E8(N) AS (SELECT 1 FROM E4 a, E4 b)   -- 1*10^8 or 100,000,000 rows

    SELECT SUM(@i) FROM E8 
    OPTION (MAXDOP 1)

平均为608ms，总计100000000个值。（即每次聚集6纳秒）

NULL

one在

sqllang.dll!CESRunTimeErrorSink::SetAggFnSkippedNull

假定设置指向消息的标志

警告：聚合或其他集合会消除空值 手术

但总体而言似乎更快（以下以毫秒为单位的运行时间）

---

当然，在这种情况下（所有输入都是

NULL

），它们会返回不同的结果，如果您想将两者互换处理，则需要

ISNULL（SUM（@i），0）

。

您能提供sql server实例的版本吗？提前感谢。@Devart RTM版本的SqlServer 2014.on 2012 sp3也会得到类似的结果。谢谢这个tipThanks，很棒的剧本！在我们的服务器（2008r2）上进行了尝试，每次5次，平均11753ms对12699ms，因此速度慢了8.04%，快了7.44%。你的平均成绩是慢8.58%或快7.91%，所以这是相似的！

sqllang.dll!CESRunTimeErrorSink::SetAggFnSkippedNull

+---------+--------+------++-------+
|         |  NULL  |  0   || Diff  |
+---------+--------+------++-------+
| Trial 1 | 7027   | 7592 || 565   |
| Trial 2 | 6981   | 7743 || 762   |
| Trial 3 | 7451   | 8015 || 564   |
| Trial 4 | 6997   | 7591 || 594   |
| Trial 5 | 7018   | 7574 || 556   |
+---------+--------+------++-------+
| Avg     | 7094.8 | 7703 || 608.2 |
+---------+--------+------++-------+