In the previous part of the chapter, you have seen the permission mechanism by which PostgreSQL allows roles (both users and groups) to access different objects within the database and data contained in the objects. In particular, with regard to tables, you have learned how to restrict access to just a specific column list within the tabular data.
PostgreSQL provides another interesting mechanism to restrict access to tabular data: row-level security. The idea is that row-level security can decide which tuples the role can gain access to, either in read or write mode. Therefore, if the column-based permissions provides a way of limiting the vertical shape of the tabular data, the RLS provides a way to restrict the horizontal shape of the data itself.
When is it appropriate to use RLS? Imagine you have a table that contains data related to users, and you don't want your users to be able to tamper with other users' data. In such a case, restricting the access...
