Why am I not able to change the "lookup" field for the Custom Object if "Labels" checkbox on the Fields page is selected?
Custom Objects, All supported versions
Lookup fields help identify records when you are working with them. Values in lookup fields are displayed on the editor’s tab when you are editing records and in the Recent Items list on the navigation pane. For example, when editing an incident, the incident’s reference number displays on the editor’s tab since Incidents.Reference # (incidents.ref_no) is configured as a lookup field in the database.
The field defined as the object lookup is automatically added as a single-field index to the object. If you do not specify a lookup field, the ID field is automatically selected as a lookup field.
Each record in the Custom Object is assigned to its unique label and if you select the Labels check box on the Fields page, the Labels field that is added to the object is automatically selected as the object’s lookup field.
Labels field is a default lookup field and once added cannot be changed unless you would like to remove it from the Custom Object.
For additional information, refer to the 'Adding fields to custom objects' section in online documentation for the version your site is currently running. To access Oracle Service Cloud manuals and documentation online, refer to the Documentation for Oracle Service Cloud Products.