how to check whether a case owner is a queue or a user? I am writing a validation rule where i need to check who is the owner of the case.
You can check if any of the User- or Queue-specific polymorphic Owner fields is empty. e.g.
will be true if the owner is a User and false if the owner is a Queue
The opposite would be:
More info about polymorphic fields here: https://developer.salesforce.com/blogs/developer-relations/2013/06/cross-object-owner-fields-a-powerful-new-formula-option.html