if you query returns multiple series the reducer function and threshold will be checked for each series.
count() means count the number of data points in each series (individually) and compare against thresholds.
sum() will sum all datapoints for each series (each series is summed individually) and compared against threshold.
If any series causes the condition to be true an alert will fire. We do not yet have per series state tracking so if one series causes the alert to trigger and then later another series casues the alert to trigger (while the alert is still in altering state) you will not be notified of the other series alerting. We do want to add per series state tracking.