I have column ID with Key. when I am using this ID in statistics box to find the total count it is showing "n/a". can anyone let me know is it possible to get total count with Key columns in statistics box.
no, that is not possible to my knowledge. The fields with the key_symbol are key_fields which link the tables. To get the count in one specific table, load the field once more with a different name so it won't be linked.
