Hi! Use a subsearch instead of appendcols. Using a subsearch, you can search for or exclude specific events based on one or more common fields.
If you want to have a list of all events in object1 which are not part of object2, try this:
index=sfdc source="sfdc_object://object1_Salesforce" NOT [search index=sfdc source="sfdc_object://object2_salesforce" | rename Case AS Id | table Id]
Looking at your current search I suppose you need to rename Case to Id in the subsearch so that the fields are the same.
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