CreateDate is a system index field maintained by Salesforce. I'd like to know when you running a query like this:
Select Id from Account Where Day_Only(CreatedDate) > exampleDate
Does the Day_Only function make the query un-selective? Is the System index used when using soql functions? Salesforce query plan says CreatedDate is indexed, but i'm not sure it is used when running the code.
I believe Salesforce does not use the index when you use Day_Only function with a custom index.