使用Select和divison零的Oracle View问题

Question

以下问题,我想在Oracle中创建一个视图,计算"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

问题:有时sw.INSTALLED_PORTS或sw.MAX_INSTALLABLE_PORTS可以为NULL(对于其他UTIL行也是如此).

有什么好方法可以做以下事情:

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

或者更短一些:

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

问候,Rob.