When I should use one to one relationship?

Question

Sorry for that noob question but is there any real needs to use one-to-one relationship with tables in your database? You can implement all necessary fields inside one table

Answer 1

not very often.

you may find some benefit if you need to implement some security - so some users can see some of the columns (table1) but not others (table2)..

of course some databases (Oracle) allow you to do this kind of security in the same table, but some others may not.