Views by irays

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									                    Joins
• Inner Joins:
• 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.
• Outer Join:
• With an outer join, records are also selected
  for which there is no entry in some of the
  tables used in the view.
                     View
•   View is a virtual table.
•   Types
•   Database view
•   Projection view
•   Help view
•   Maintenance view
              Database view

-Can be developed on single table or multiple tables
-Database views implement an inner join.
-Only read access is permitted for database views
   that are defined over several tables.
-If a database view contains only one single table,
   data can be inserted in this table with the view.
-A database view may only contain transparent
   tables
           Projection View
• Projection views are used to hide fields of a
  table.
• A projection view contains exactly one
  table .Hence no joins
• You cannot define selection conditions for
  projection views.
• You can also access pooled tables and
  cluster tables with a projection view.
                Help view
• You have to create a help view if a view
  with outer join is needed as selection
  method of a search help
• If you need a view with outer join for the
  data selection, you have to use a help view
  as selection method.
• All the tables included in a help view must
  be linked with foreign keys.
            Maintenance View
• It uses outer join
• Maintenance views offer easy ways to maintain
  complex application objects.
• A maintenance view permits you to maintain the
  data of an application object together. The data is
  automatically distributed in the underlying
  database tables.
• All the tables in a maintenance view must be
  linked with foreign keys

								
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