Am using this search
index=level3 host=Test | chart count over "Opened" by "Assignment group"
I am getting the desired result in statistics but not in visualization.
Am not able to post any pictures so pls mail me i will reply back.
Which visualization are you using? Have you set it to one of the chart types (bar, line, area) or a format that is compatible with the data?
Please try..capital over and by.
index=level3 host=Test | chart count OVER "Opened" BY "Assignment group"
your mail id is not available on your profile ..