Datadictionary (se11) why do we need view?explain?

Question

hi
1 why do we need view?
2 .what is the difference between view & inner join?
3.tell me about view types?
regards
eswar

Answer 1

Use of Views instead of base tables
Many times ABAP programmers deal with base tables and nested selects. Instead it is always advisable to see whether there is any view provided by SAP on those base tables, so that the data can be filtered out directly, rather than specially coding for it.
Not recommended
            Select * from zcntry where cntry like ‘IN%’.
             Select single * from zflight where cntry = zcntry-cntry and airln = ‘LF’.
            Endselect.
Recommended
            Select * from zcnfl where cntry like ‘IN%’ and airln = ‘LF’.
            Endselect.
Joins
Proper use of Inner Join
When multiple SAP tables are logically joined, it is always advisable to use inner join to read the data from them. This certainly reduces the load on the network.
Let us take an example of 2 tables, zairln and zflight. The table zairln has the field airln, which is the airline code and the field lnnam, which is the name of the airline. The table zflight has the field airln, the airline code and other fields which hold the details of the flights that an airline operates.
Since these 2 tables a re logically joined by the airln field, it is advisable to use the inner join.
             Select aairln alnnam bfligh bcntry into table int_airdet
            From zairln as a inner join zflight as b on aairln = bairln.
In order to restrict the data as per the selection criteria, a where clause can be added to the above inner join.
What is the Different Types and Usage of Views
This is often asked in an interview about the types of views:
The followings are different types of views:
- Database View   (SE11)
Database views are implement an inner join, that is, only records of the primary table (selected via the join operation) for which the corresponding records of the secondary tables also exist are fetched. Inconsistencies between primary and secondary table could, therefore, lead to a reduced selection set.
In database views, the join conditions can be formulated using equality relationships between any base fields. In the other types of view, they must be taken from existing foreign keys. That is, tables can only be collected in a maintenance or help view if they are linked to one another via foreign keys.
- Help View    ( SE54)
Help views are used to output additional information when the online help system is called.
When the F4 button is pressed for a screen field, a check is first made on whether a matchcode is defined for this field. If this is not the case, the help view is displayed in which the check table of the field is the primary table. Thus, for each table no more than one help view can be created, that is, a table can only be primary table in at most one help view.
- Projection View
Projection views are used to suppress or mask certain fields in a table (projection), thus minimizing the number of interfaces. This means that only the data that is actually required is exchanged when the database is accessed.
A projection view can draw upon only one table. Selection conditions cannot be specified for projection views.
- Maintenance View   ( SE54 )
Maintenance views enable a business-oriented approach to looking at data, while at the same time, making it possible to maintain the data involved. Data from several tables can be summarized in a maintenance view and maintained collectively via this view. That is, the data is entered via the view and then distributed to the underlying tables by the system.
regards,
srinivas
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