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Answer Posted / subhajit guha
View in sql called the virtual table.Physically it has no
existance, so that it don't occupy the space.It retrives
the data from original table at runtime.
Views are stored in ORACLE system catalog.
Basically, in realtime environment views are used to
protect the main table for operation.Besides for security
purpose view must be used.i.e. one user can hide the main
tale from other user for creating view.
On basic of creation of view, it is divied into two pars....
1. Simple view: In that case columns for same table(single
table) are fetched for creating a view.
Syntax: SQL>create view <view_name> as select <column
name1.column name2....> from table where <condition>;
2. Complex view: Columns are fetched from different tables
on basis of operation would perform.Generally for join
operation it is used.
Syntax: SQL>create view <view_name> as select <col1..coln
from table 1>,<col 1..col n for table 2>....< .. for table
n> from table 1,..,table n where <condition>;
On basis of operations on view ... it is divided inti two
parts:
1. Read only view, 2. Updatable view
** incase of updatable view insertion,deletion and updation
can be done...... aggregation,rowid,rownum and any group
function cann't be performed.
** incase of read only view, only view canbe read, no DML
operations cann't be perfomed.
to drop a view ..... we use:
SQL>drop view <view_name>;
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