Question

考虑这个问题：

WITH Scores (score)
     AS
     (
      SELECT CAST(score AS INTEGER)
        FROM (
              VALUES (0), 
                     (10), 
                     (10)
             ) AS Scores (score)
     )
SELECT AVG(CAST(score AS DECIMAL(19, 8))) AS precision_eight, 
       AVG(CAST(score AS DECIMAL(19, 7))) AS precision_seven, 
       AVG(CAST(score AS DECIMAL(19, 6))) AS precision_six, 
       AVG(CAST(score AS DECIMAL(19, 5))) AS precision_five, 
       AVG(CAST(score AS DECIMAL(19, 4))) AS precision_four
  FROM Scores;

结果：

precision_eight | precision_seven | precision_six | precision_five | precision_four 
     6.66666666 |       6.6666666 |      6.666666 |       6.666666 |       6.666666

为什么我总是得到至少六位小数？这是记录在案的行为？

（我正在运行SQL Server 2008）

Answer 1

小数的AVG始终返回“十进制（38，s）除以十进制（10,0）”数据类型（see here）

您必须将AVG结果转换为所需的精度。

Answer 2

我准备发布与Jappie's answer类似的内容以及此示例，以说明幕后发生的事情。

declare @a int
set @a = 0
declare @b int
set @b = 10
declare @c int
set @c = 10

declare @n decimal(10,0)
set @n = 3

select cast((@a+@b+@c) as decimal(38,4))/@n

为什么将AVG（整数列）转换为DECIMAL至少返回六位小数？

2 个答案: