Views

• Views, Match code objects ( Search Help ), lock objects etc. is known as aggregated objects.
• Using Views, We can permit access to certain set of data from a table or a set of tables in an application. 
• In other words Views are a logical data sets which contain data extracted from a single table or multiple tables as a single entity.
• These objects are based on tables.
• The data for an application object is often distributed on several DB tables in a relational data model.
• The database systems therefore permit you to define application-dependent views on the data.
• In this way, data from different tables can be combined in a logical manner and information which is not of interest can be masked out.
• Aggregate objects in the ABAP/4 Dictionary are objects, which are formed from several tables.
• Views are application-dependent displays of various ABAP/4 Dictionary tables.
• Views make it possible to provide the user with information from fields of various tables required when working with the R/3 System.
• Views are used mainly for programming with ABAP/4 and for the F4 help.
• Views are used to represent data which is distributed between many tables.
• Data of a view is not actually physically stored. 

• There are 4 types of views

1. Database View
2. Projection View
3. Maintenance View
4. Help View.

• The individual tables involved in a view should be linked with a relational join operation.
• The data that is selected using a view depend on whether the views implement an inner join or an outer join. 
• Database views implement Inner Join .
• Maintenance Views  and Help Views implement an outer join.
• Using the inner join, we can retrieve records which are there in the entire table involved in the view i.e. we only get the records of the primary table which also have the same record in the secondary tables of the view.
• Using an outer join we can also select the records for which there are no entries in the secondary tables.

Note :

• The join conditions for database views can be formulated using equalityrelationships between any base fields. 
• The join conditions for the other view types must be obtained from existing foreign keys.
• Tables therefore can only be combined into a maintenance view or help view if they are linked to one another with foreign keys.

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