tsql - 遇到除以零错误。T-SQL

Question

我有以下在 SQL 2012 中运行的 T-SQL

SELECT machine_id, speed_gps_kph, odometer_total, event_timestamp, 
   1.0 * (speed_gps_kph - LAG(speed_gps_kph, 1) OVER (PARTITION BY machine_id ORDER BY event_timestamp)) /
   datediff(ss, LAG(event_timestamp, 1) OVER (PARTITION BY machine_id ORDER BY event_timestamp), event_timestamp)
FROM   Simple_speed

但是，正如错误所示，我遇到了除以零的问题。

关于这个问题有很多帖子和答案，但我很难开始工作。

Answer 1

这是一种控制被零除错误的简单方法，无需重复自己，使用NULLIF(...,0)：

SELECT machine_id, speed_gps_kph, odometer_total, event_timestamp, 
   1.0 * (speed_gps_kph - LAG(speed_gps_kph, 1) OVER (PARTITION BY machine_id ORDER BY event_timestamp)) 
   / NULLIF(datediff(ss, LAG(event_timestamp, 1) OVER (PARTITION BY machine_id ORDER BY event_timestamp), event_timestamp),0)
FROM Simple_speed

该表达式现在将返回NULL分母为零的行。