除以零錯誤的SQL

Question

我使用以下方法得到除以零的錯誤：

Select Top 100 *, Case (a.value)
    When 0.0
    Then Null
    Else ((cast(b.value as decimal) - cast(a.value as decimal))/cast(a.value as decimal)) * 100
    End
    as 'Montly Price Change (%)'
From AllProducts a
Join AllProducts b
On a.series_id=b.series_id And (b.Date = DATEADD(month, 1, a.Date))

我找不到解決此問題的方法。

Select Top 100 *, Case cast((a.value) as decimal)
    When 0.0
    Then Null
    Else ((cast(b.value as decimal) - cast(a.value as decimal))/cast(a.value as decimal)) * 100
    End
    as 'Montly Price Change (%)'
From AllProducts a
Join AllProducts b
On a.series_id=b.series_id And (b.Date = DATEADD(month, 1, a.Date))

但這出於某種原因使我的整個列為空。

Answer 1

除以NULL的任何數字都會得到NULL，並且不會產生錯誤。

Select Top 100 *, Case cast((a.value) as decimal)
        When 0.0
        Then Null
        Else ((cast(b.value as decimal) - cast(a.value as decimal))/NULLIF(cast(a.value as decimal)),0) * 100
        End
        as 'Montly Price Change (%)'
    From AllProducts a
    Join AllProducts b
    On a.series_id=b.series_id And (b.Date = DATEADD(month, 1, a.Date))

如果您想返回零

COALESCE(cast(a.value as decimal))/NULLIF(cast(a.value as decimal)),0),0)

Answer 2

使用NULLIF將起作用

Select Top 100 *,
    ((cast(b.value as decimal) - cast(a.value as decimal))/NULLIF(cast(a.value as decimal),0)) * 100

    as 'Montly Price Change (%)'
From AllProducts a
Join AllProducts b
On a.series_id=b.series_id And (b.Date = DATEADD(month, 1, a.Date))

Answer 3

我認為“小數”類型的默認小數位數（小數點后的位數）為0。因此，表達式中小於<1的分母總是求值為0。嘗試使用小數（10 ，3）。

Answer 4

我猜您的值都小於1？ 十進制小數位數的默認值為0。因此，如果您的值小於1，則它們都將轉換為0。您可以使用cast(a.value as decimal(<precision>,<scale>)) ，也可以強制浮動。

這樣的事情應該起作用：

Select Top 100 *,
    (cast(b.value as float) - cast(a.value as float))/cast(nullif(a.value,0) as float)) * 100 as 'Montly Price Change (%)'
From AllProducts a
Join AllProducts b
On a.series_id=b.series_id And (b.Date = DATEADD(month, 1, a.Date))