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:
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。
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