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The entire cross product is not usually a sensible selection. The cross product must therefore be restricted with join conditions. A join condition describes how the records of the two tables are connected.
Inner Join and Outer Join
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 only get the records of the cross-product for which there is an entry in all tables used in the view. With an outer join, records are also selected 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 therefore be a subset of the hits determined with an outer join.
Database views implement an inner join. The database therefore only provides those records for which there is an entry in all the tables used in the view. Help views and maintenance views, however, implement an outer join.
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 only get the records of the cross-product for which there is an entry in all tables used in the view. With an outer join, records are also selected 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 therefore be a subset of the hits determined with an outer join.
Database views implement an inner join. The database therefore only provides those records for which there is an entry in all the tables used in the view. Help views and maintenance views, however, implement an outer join.
Bluesky
