Question

我有一个变量，我希望在小数点左边返回最多5个，并且总是在右边3个

CONVERT(VARCHAR(14),CONVERT(DECIMAL(8,3),
        DATEDIFF(MILLISECOND,@ProcessTime,GETDATE()))/@OneThousand)

现在变量定义为

DECLARE @ProcessTime DATETIME 
DECLARE @OneThousand DECIMAL(8,3)
SET @OneThousand = 1000.000

这总是返回类似

的内容

0.003000000000

我想我可以用左功能解决我的问题，但我的问题是为什么会发生这种情况。如果定义的最小小数变量@OneThousand为3，那么返回值是否应该有3位小数？

Answer 1

将DECIMAL(8,3)除以DECIMAL(8,3)的结果给出了DECIMAL(20,12)的数据类型以查看此内容

DECLARE @ProcessTime DATETIME =getdate()
DECLARE @OneThousand DECIMAL(8,3)
SET @OneThousand = 1000.000

DECLARE @v SQL_VARIANT

SET @v = CONVERT(DECIMAL(8,3),
        DATEDIFF(MILLISECOND,@ProcessTime,GETDATE()))/@OneThousand

SELECT
    CAST(SQL_VARIANT_PROPERTY(@v, 'BaseType') AS VARCHAR(30)) AS BaseType,
    CAST(SQL_VARIANT_PROPERTY(@v, 'Precision') AS INT) AS Precision,
    CAST(SQL_VARIANT_PROPERTY(@v, 'Scale') AS INT) AS Scale

BOL部分解释了decimal(20,12) is here

的原因

Operation:        e1 / e2
Result precision: p1 - s1 + s2 + max(6, s1 + p2 + 1)
Result scale:     max(6, s1 + p2 + 1)

所以在你的情况下

Result precision: 8 - 3 + 3 + max(6, 3 + 8 + 1) = 20
Result scale:     max(6, 3 + 8 + 1)             = 12

Answer 2

...试

SELECT CAST(DATEDIFF(ms, @processDate, GETDATE()) / 1000.000 AS decimal(8,3))

Sql Server有效数字

2 个答案: