Field not appearing in Group by in Report

[Steve R]

We have a custom application built.  A user wants to group by a specific field in a pie chart from the table selected.  That field is on that table and not on a referenced table.  The field does not appear in the 'Group by' select BUT appears in the 'additional group by' option.  

She wants to export the report grouped by that field but since it is in the additional group by, ServiceNow does not have the ability to export in the 'additional group by', only via a JPG/PNG and those cut off some of the information.

Any ideas on why that field only appears in the 'Additional group by'?

[Steve R]

Thanks for your assistance.  I'm not sure I understand what you mean by unlimited possibilities (strings and numbers)  Can you provide me an example of what you mean?  

Would it be that records with choices, references produce one results in a single field for each record where a list actually has multiple results in a single field for one record?

[Brian Lancaster · Accepted solution]

So for example when you have a list field.  there is an untold number of possibilities what can appear in that filed.   It will most likely never be the same.  Say you have it pointing to the user table like the watch list.  One ticket could have user a, b, c, d, e, f, g, h and another ticket could have user a, b and then another ticket could have user x, y, z.  Hopefully you are getting the picture.  Group by is meant for things that can be consistent like the caller filed because you will only ever have one caller in that field for each record.  Then string fields like short description can also have an untold number of different characters.  Hope this helped. 

[tleonard]

I have a custom field (type = list) that doesn't appear for selection in group by on my new report (incident table). Is there any other property or configuration I can check to make it appear for selection. The field has only 14 unique choices.