I'm trying to use an aggregate query, but one of the fields I want to group by is not groupable (saw it in the soql error and then verified groupable=false in the metadata).
It's just a number field that holds an integer (number 2,0 in salesforce field spec-speak).
Is there a trick to make it groupable? Any way around this problem? I don't want to write hundreds of lines of code just to average a list by this field.
I'm not 100% sure what makes it "groupable". The Considerations When Using GROUP BY does mention it:
Some object fields have a field type that does not support grouping. You can't include fields with these field types in a GROUP BY clause. The Field object associated with DescribeSObjectResult has a groupable field that defines whether you can include the field in a GROUP BY clause.
Although not exactly elegant, you could try to copy the not groupable field to a groupable field via a workflow rule and then group by that one instead.
It appears that you can not group by custom number fields and not the ability to group by formulas is a request on the ideaexchange so you will need to create a workflow rule that copies the number to a text field.
Note that most standard number fields cannot be grouped by as well but a few like account.numberofemployees can be.
For those people who come across this old but still relevant question, see the more complete community wiki answer here
