When creating custom fields, and custom field groups, I have fallen into two pit falls.
First, the name of a custom field should not exceed a certain length, causing malfunction in the SQL structure.
Second, values should be unique. Of course, you would say, but look at this example: values: 1,2,3,4,5,6,7,8,9,10,11,12. When showing the values in a report, the 2 will show for both 2 and 12, and value 1 will show for 1,10,11 and 12.
The question is, what things should be considered when creating custom fields?