Own is a strange term, because really there is just one user that is listed as owner, but there are there are three users who essentially are owner level, super-powered users in a database:
1. A login using server rights, usually via the sysadmin server role (or a server permission to view all data)
2. The user dbo in a database, acquired either as a sysadmin, or as being the user listed as the owner of the database
3. Members of the db_owner database role
Sometimes, in the context of a database, these all start to blur together. But they are definitely all three independent things. Let’s write some code and see the differences, and one of the cases may be surprising to you. To do this, I will just be using the SELECT permission on a single table, but other rights will generally behave similarly. Note that another tool in your toolbox is Row Level Security in SQL Server 2016+. It is different, in that you can include a predicate that excludes the dbo, which you can read more about here in some of my earlier blogs.