The data that can be selected with a view depends primarily on whether the view implements an inner join or an outer join. With an inner join, you get only the records of the cross-product for which there is an entry in all tables used in the view. With an outer join, the system also selects records for which there is no entry in some of the tables used in the view.
The set of hits determined by an inner join can be a subset of the hits determined with an outer join.
Database views implement an inner join. The database view provides only those records for which there is an entry in all the tables used in the view. Help views and maintenance views implement an outer join. You can see an example of an inner and outer join in the following figure.