在sql中计算非零值

时间:2013-05-27 14:13:46

标签: sql sql-server

我正在尝试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:

  • Bob Smith 62 62 62
  • Nathan Jones 65 65 65

我正在尝试在每个单独的值中计算非零值。每个违规都应该单独分组。

2 个答案:

答案 0 :(得分:17)

使用NULLIF将零更改为NULL,计数忽略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,因此不需要 WHERE和HAVING子句

答案 1 :(得分:7)

使用case语句将过滤谓词[s]放在Sum()函数内是一个有用的技巧,只要你需要根据某个谓词条件计算项目。

Select DriverName,
    Sum(case When over_rpm > 0 Then 1 Else 0 End) OverRpm,
    Sum(case When over_spd > 0 Then 1 Else 0 End) OverSpeed,
    Sum(case When brake_events > 0 Then 1 Else 0 End) BrakeEvents,
    etc.
FROM performxbydriverdata
Group By DriverName