Are you saying that:
- You have multiple date_read columns in each book?
- You want to know if any of these columns in a single book contain the same value?
- By "same value" do you mean exactly the same value (date & time), do you mean the same day, the same time, or do you mean something else?
This can be done with a template search. If you tell me the column lookup names and answer the above questions then I will give you an example.
Probably one of DaltonST's plugins, for example multi-column search, can do this, but I don't know how to use it.