Oracle查看問題與選擇和divison零

Question

以下問題，我想在Oracle中創建一個視圖，以計算「利用率百分比」。

AS SELECT 
    sw.SWITCH_ID, 
    sw.ASSET_ID, 
    sw.SYSTEMNAME, 
    sw.MAX_INSTALLABLE_PORTS, 
    sw.INSTALLED_PORTS, 
    sw.USED_PORTS, 
    (sw.INSTALLED_PORTS/sw.MAX_INSTALLABLE_PORTS)*100 AS UTIL_INSTALLED_PORTS, 
    sw.RES_INFRASTRUCTURE_PORTS, 
    sw.USED_INFRASTRUCTURE_PORTS, 
    sw.FREE_INFRASTRUCTURE_PORTS, 
    (sw.INSTALLED_PORTS/sw.MAX_INSTALLABLE_PORTS)*100 AS UTIL_INFRASTRUCTURE_PORTS, 
    sw.RESERVED_DEVICE_PORTS, 
    sw.USED_DEVICE_PORTS, 
    sw.FREE_DEVICE_PORTS, 
    (sw.FREE_DEVICE_PORTS/sw.RESERVED_DEVICE_PORTS)*100 AS UTIL_DEVICE_PORTS, 
    sw.RUN_DATE 

問題：有時sw.INSTALLED_PORTS或sw.MAX_INSTALLABLE_PORTS可以爲NULL（同爲其他UTIL行）..

有沒有什麼好的辦法做這樣的事情：

if (sw.INSTALLED_PORTS or sw.MAX_INSTALLABLE_PORTS == null) 
     UTIL_INSTALLABLE_PORTS = null 
else (sw.INSTALLED_PORTS/sw.MAX_INSTALLABLE_PORTS)*100 AS UTIL_INSTALLABLE_PORTS, 

Answer 1

NULL的分割與零分割不同（因爲您引用標題中的問題）。

select 1/null from dual = NULL
​​= NULL

所以，你會自動得到你想要的東西(sw.INSTALLED_PORTS/sw.MAX_INSTALLABLE_PORTS)*100。

我認爲，問題是當sw.MAX_INSTALLABLE_PORTS爲零。在這種情況下，你可以使用以下命令：

case 
    when sw.MAX_INSTALLABLE_PORTS = 0 then null 
    else (sw.INSTALLED_PORTS/sw.MAX_INSTALLABLE_PORTS)*100 
end 

Answer 2

CASE 
    WHEN sw.INSTALLED_PORTS IS NULL OR sw.MAX_INSTALLABLE_PORTS IS NULL THEN NULL 
    ELSE (sw.INSTALLED_PORTS/sw.MAX_INSTALLABLE_PORTS)*100 
END UTIL_INFRASTRUCTURE_PORTS 

Answer 3

您可以使用COALESCE（）從其參數返回第一個非空，如：

(COALESCE(sw.INSTALLED_PORTS, 0)/COALESCE(sw.MAX_INSTALLABLE_PORTS,1))*100 
AS UTIL_DEVICE_PORTS 

請注意，我使用1作爲分母中的coalesce默認值，您不需要DIVIDE/0。

Answer 4

或短一點：

sw.INSTALLED_PORTS/NULLIF(sw.MAX_INSTALLABLE_PORTS,0) 

問候， 羅布。