在sql中计算非零值

我试图计算每个列大于零的总次数,按驱动程序名称分组.现在我有;

SELECT drivername
      , COUNT(over_rpm)      AS RPMViolations
      , COUNT(over_spd)      AS SpdViolations
      , COUNT(brake_events)  AS BrakeEvents
  FROM performxbydriverdata
 WHERE  over_rpm > 0
    OR over_spd > 0
    OR brake_events > 0
GROUP BY drivername

这给了我所有的非零值,但我得到一个显示为:

>鲍勃史密斯62 62 62
>内森琼斯65 65 65
>等

我试图在每个单独的值中计算非零值.每个违规都应该单独分组.

使用NULLIF将零更改为NULL,count忽略NULL

SELECT drivername,
     COUNT(NULLIF(over_rpm,0)) AS RPMViolations,
     COUNT(NULLIF(over_spd,0)) AS SpdViolations,
     COUNT(NULLIF(brake_events,0)) AS BrakeEvents
FROM performxbydriverdata
GROUP BY drivername;

您也可以使用此组删除WHERE子句以提高性能
由于匹配好的索引,OR条件经常运行得很糟糕

使用HAVING(根据其他答案)将删除所有3个聚合为零的行,这些行可能对您有用,也可能对您没用.如果需要,您可以添加此项.说,WHERE意味着至少有一行具有非零值,因此您不需要WHERE和HAVING子句

翻译自:https://stackoverflow.com/questions/16775115/counting-non-zero-values-in-sql

转载注明原文:在sql中计算非零值