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Derived Tables:How a derived table is useful than a view in data base? What are the additional features

derived table provides?

Derived tables are tables that you define in the universe schema . You create objects on

them as you do with any other table. A derived table is define by an !" #uery at the

universe level that can be used as a lo$ical table in Desi$ner.

Derived tables have the followin$ advanta$es:

%educed amount of data returned to the document for analysis.You can include comple& calculations and functions in a derived table. These operations

are performed before the result set is returned to document ' which saves time and

reduces the need for comple& analysis of lar$e amounts of data at the report level.

%educed maintenance of database summary tables.

Derived tables can ' in some cases' replace statistical tables that hold results for comple&calculations that are incorporated into the universe usin$ a$$re$ate awareness. These

a$$re$ate tables are costly to maintain and refresh fre#uently. Derived tables can return

the same data and provide real time data analysis.

Derived tables are similar to database views' with the advanta$e that the !" for

a derived table can include (usiness )bjects *rompts.

+iew,Data (ase-:

n databasetheory' a view consists of a stored #ueryaccessible as a virtual table

composed of the result set of a#uery. /nli0e ordinary tables ,base tables- in a relational

database'a view does not form part of thephysical schema: it is a dynamic' virtual tablecomputed or collated from datain the database. 1han$in$ the datain a tablealters the

datashown in subse#uent invocations of the view.

+iews can provide advanta$es over tables:

+iews can represent a subset of the data contained in a table+iews canjoinand simplify multiple tables into a sin$le virtual table

+iews can act as a$$re$ated tables' where the database en$ine a$$re$ates data ,sum'

avera$eetc- and presents the calculated results as part of the data+iews can hide the comple&ity of data2 for e&ample a view could appear as ales3444 or

ales3445' transparentlypartitionin$the actual underlyin$ table

+iews ta0e very little space to store2 the database contains only the definition of a view'not a copy of all the data it presents

Dependin$ on the !"en$ine used' views can provide e&tra security

+iews can limit the de$ree of e&posure of a table or tables to the outer world

http://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Database_theoryhttp://en.wikipedia.org/wiki/Database_queryhttp://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Query_languagehttp://en.wikipedia.org/wiki/Query_languagehttp://en.wikipedia.org/wiki/Relational_databasehttp://en.wikipedia.org/wiki/Relational_databasehttp://en.wikipedia.org/wiki/Relational_databasehttp://en.wikipedia.org/wiki/Database_designhttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Join_(SQL)http://en.wikipedia.org/wiki/Join_(SQL)http://en.wikipedia.org/wiki/Join_(SQL)http://en.wikipedia.org/wiki/Sumhttp://en.wikipedia.org/wiki/Averagehttp://en.wikipedia.org/wiki/Averagehttp://en.wikipedia.org/wiki/Partition_(database)http://en.wikipedia.org/wiki/SQLhttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Database_theoryhttp://en.wikipedia.org/wiki/Database_queryhttp://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Query_languagehttp://en.wikipedia.org/wiki/Relational_databasehttp://en.wikipedia.org/wiki/Relational_databasehttp://en.wikipedia.org/wiki/Database_designhttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Databasehttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Table_(database)http://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Join_(SQL)http://en.wikipedia.org/wiki/Sumhttp://en.wikipedia.org/wiki/Averagehttp://en.wikipedia.org/wiki/Partition_(database)http://en.wikipedia.org/wiki/SQL

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6ust as functions,in pro$rammin$- can provide abstraction' so database users can create

abstraction by usin$ views. n another parallel with functions' database users can

manipulate nested views' thus one view can a$$re$ate data from other views. Without theuse of views the normali7ation of databases above second normal formwould become

much more difficult. +iews can ma0e it easier to create lossless join decomposition.

6ust as rows in a base table lac0 any defined orderin$' rows available throu$h a view donot appear with any default sortin$. A view is a relational table' and the relational model

defines a table as a set of rows. ince sets are not ordered 8 by definition 8 the rows in a

view are not ordered' either. Therefore' an )%D9% (Yclause in the view definition ismeanin$less. The !" standard ,!":344- does not allow an )%D9% (Y clause in a

subselect in a 1%9AT9 +9W statement' just as it is not allowed in a 1%9AT9 TA("9

statement. However' sorted data can be obtained from a view' in the same way as any

other table 8 as part of a #uery statement.;evertheless' some D(

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/niverse *arameters:

What are universe parameters? What does the parameters tab in universe

parameter indicate?

The parameter tab in the universe indicates list of !" parameters that can be set

to optimi7e !" $eneration. The parameter file is still used for many %D(

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What are nde&es?

earch Eoo$le under )racle 1oncepts