如何得到這個十進制值，而不是空

Question

我想獲得價值小數在此查詢，但無法得到我收到NULL值

SELECT CAST(CAST(CAST(SUM(CAST(0 AS INT)) AS DECIMAL(10, 2)) * 100 
/CAST(NULLIF(SUM(CAST(0 AS INT)) 
+ SUM(CAST(0 AS INT)) + 
SUM(CAST(0 AS INT)), 0) 
AS DECIMAL(10, 2)) AS DECIMAL(10, 2)) AS DECIMAL) 

如何讓輸出

0.00 

，而不是空在此查詢

Answer 1

使用ISNULL內置函數：

ISNULL(CAST(CAST(CAST(SUM(CAST(0 AS INT)) AS DECIMAL(10, 2)) * 100/CAST(NULLIF(SUM(CAST(0 AS INT)) + SUM(CAST(0 AS INT)) + SUM(CAST(0 AS INT)), 0) AS DECIMAL(10, 2)) AS DECIMAL(10, 2)) AS DECIMAL), 0) 

http://technet.microsoft.com/es-es/library/ms184325.aspx

Answer 2

我甚至不先來了解所有你正在做的轉換，但你可以只是簡單的對錶達式中使用ISNULL：

SELECT ISNULL(<all your calculations here>,0) 

Answer 3

太多的強制類型轉換在SQL

使用情況下，如果你不希望使用ISNULL，這是必要的，因爲你有NULLIF

SELECT 
    CAST(
    CASE 
     WHEN SUM(CAST(0 AS INT)) + SUM(CAST(0 AS INT)) + SUM(CAST(0 AS INT)) = 0 THEN 0 
     ELSE SUM(CAST(0 AS INT)) * 100.00/(SUM(CAST(0 AS INT)) + SUM(CAST(0 AS INT)) + SUM(CAST(0 AS INT))) 
    END 
    AS DECIMAL(10, 2)) 

無論如何，除以零的任何東西都是未定義的或無窮大的：不爲零。

Answer 4

整個表達式計算爲NULL，因爲您正在使用以下代碼。

NULLIF (
    SUM ( 
     CAST(0 AS INT) 
    ) + 
    SUM( 
     CAST(0 AS INT) 
    ) + 
    SUM( CAST(0 AS INT) 
    ), 
    0 
) 

我打算稍微分解一下，以便更容易理解。

CAST(0 AS INT) evaluates to 0 

SUM(CAST(0 AS INT)) evaluates to 0 

SUM(CAST(0 AS INT)) + 
SUM(CAST(0 AS INT)) + 
SUM(CAST(0 AS INT)) also evaluates to 0 

因此，將整個表達式包裝成NULLIF（表達式0）意味着它作爲NULL出現。

null然後傳播通過計算的其餘部分，並導致整個表達式計算爲NULL。

如果您希望它爲0，則應將整個表達式包裝在ISNULL或COALESCE語句中，或者可以刪除NULLIF檢查，儘管它有點不清楚您實際嘗試實現的內容。