view created on two or more tables using inner join concepts. you can not maintain the data and you can only read the data.
view created on single table.
mainly used to minimize the database interface and improve the performance of system. You can maintain the data in project view. This view supports insert, update, delete and select operators.
created on two or more tables using outer join concepts. You can not execute help views directly, instead you have to include help views inside the search helps. It provides help functionary F4 for an input field.
used in SAP for internal purpose. It helps in creating the maintenance data and the data can be distributed into several tables. In real time we do not create maintenance views because the data multiple tables leads to inconsistency.
If you need to extract the data from different tables with desired fields, then you need to create a view of the required fields.
Tcode to create ABAP views