I would not expect the standard SQL behavior (ignoring nulls and averaging the rest of the values) to result in what I am seeing in the graphs, but you are probably right that I am going to have to define a specialty aggregation.
On Saturday, June 3, 2023 at 8:10:26 PM UTC-4 Tom Keffer wrote: > WeeWX uses a SQL statement to calculate the averages. SQL ignores any > nulls in an aggregate interval. So, if there is nothing but nulls in an > interval, the result will be null, not zero. > > Null values signify unknown values, not zero. I didn't follow the > discussion of your service, but if you can't change it to store zero when > the value is, well, zero, then you'll have to define your own specialty > xtype aggregations, which treats null as a zero, perhaps by using the SQL > function IFNULL(). > > Instructions on defining custom xtype aggregations: > https://github.com/weewx/weewx/wiki/xtypes#calculating-aggregates > > > On Sat, Jun 3, 2023 at 4:39 PM 'Peter Fletcher' via weewx-user < > weewx...@googlegroups.com> wrote: > >> For reasons discussed elsewhere, I have a user service which saves nulls. >> rather than zeros to the archive records for UV and solar radiation values >> during the night. Daily and weekly graphs continue to look as they should >> (with the daytime tracings arising from at or very near to the zero axis). >> On the monthly graphs, however, the tracings do not touch the zero axis at >> either end of the daytime peak, I am guessing that, in calculating averaged >> data points for the longer term graphs, weewx is treating the average of >> any group of values that contains a null value as null. There is some logic >> to this, but the results are unhelpful in this case. Am I right about the >> cause of the problem, and is there a workaround for it? >> >> -- >> You received this message because you are subscribed to the Google Groups >> "weewx-user" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to weewx-user+...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/weewx-user/aff03e49-1c45-4383-bc80-a3db9425ac8fn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/weewx-user/aff03e49-1c45-4383-bc80-a3db9425ac8fn%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to weewx-user+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/0f0dab2d-ad9f-4297-a5db-c87c23981ae8n%40googlegroups.com.
