Mohan
Answered On : Jun 2nd, 2006
Hi,
Advantages of views:
1. View the data without storing the data into the object.
2. Restict the view of a table i.e. can hide some of columns in the tables.
3. Join two or more tables and show it as one object to user.
4. Restict the access of a table so that nobody can insert the rows into the table.
Disadvatages:
1. Can not use DML operations on this.
2. When table is dropped view becomes inactive.. it depends on the table objects.
3. It is an object, so it occupies space.
Pls. add , if I miss any of them.
Thanks,
Mohan
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hi,
Just to add ..Views don't consume space as they are created dynamically ...ex- when you do select * from view_name ;
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You can update (DML) a table through a view if the view is created using a single table. If the view is created using multiple tables, then if the tables are normalised using constraints, you could update those tables too through the view.
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The inline view is a construct in Oracle SQL where you can place a query in the SQL FROM, clause, just as if the query was a table name.
select
fs.tablespace_name "Tablespace",
(df.totalspace - fs.freespace) "Used MB",
fs.freespace "Free MB",
df.totalspace "Total MB",
round(100 * (fs.freespace / df.totalspace)) "Pct. Free"
from
(select
tablespace_name,
round(sum(bytes) / 1048576) TotalSpace
from
dba_data_files
group by
tablespace_name
) df,
(select
tablespace_name,
round(sum(bytes) / 1048576) FreeSpace
from
dba_free_space
group by
tablespace_name
) fs
where
df.tablespace_name = fs.tablespace_name;
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advantages
1. hiding the data.
2. you can use two tables data in view.
3. security will be there.
disadvantages
1.when table is not there view will not work.
2. dml is not possible if that is more than one table.
3. it is also database object so it will occupy the space.
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YOGENDRA SHRIVASTAVA
Answered On : Nov 26th, 2006
hello sir,
plz clear that. is view has storage space. if not then y u written this
"it is also database object so it will occupy the space."
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Thulasidas
Answered On : Nov 26th, 2006
another disadvantage of a view is, it affects performance. Querying from view takes more time than directly querying from the table
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Indira
Answered On : Dec 2nd, 2006
Hi,Only the view definition is stored as a select statement in the data dictionary. Each time a view is accessed the select statement is executed and the rows are retrieved. It does not own data of its own ,so occupies negligable amount of space. It is also useful in hiding some columns from the original tables and the user can be restrictedfrom viewing all the columnsIndira
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DHRUVA SEN GUPTA
Answered On : Apr 26th, 2007
View based on multiple tables are up-datable using INSTEAD OF triggers.
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shalini parekh
Answered On : Nov 14th, 2011
hi!
i would like to add another point to the disadvantages of view...
DISADVANTAGES OF VIEW:
A query fired on a view will run slower than a query fired on a base table ,this is because the view definition has to be retrieved from the oracle's system catalog,the base table has to identified and opened in memory and then view has to be constructed on the top of the base table,suitably masking table columns
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Pralay
Answered On : May 29th, 2012
View needs very less space. Only view definition needs the database space where it does not store any data in it.
1 User has rated as useful.
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View is a virtual table. when base table is deleted then view is not in use.
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Sarvesh
Answered On : Aug 24th, 2012
Views does not require any space in the database.
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millar
Answered On : Sep 13th, 2012
some view cannot be updated when it contains group by,order by clauses, which are said to be non updatable views, this type of view can be updated using INSTEAD OF TRIGGERS , the purpose of instead of triggers when a dml statement is issued against a view, instead of updating the trigger, instead of trigger will update the bast table containing the view
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Sadashiv
Answered On : Nov 14th, 2012
Views do not actually store the data. So only for the view definition the space is required of the database.
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vin
Answered On : Nov 22nd, 2012
We can perform DML operations on view
and a view does not occupy any physical space in db.
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purna chandrudu
Answered On : May 13th, 2013
DML operation can performed on views.
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soumya
Answered On : May 17th, 2013
View when called always contacts the base table, on which it is built to get the data .so it always goes to the server thats why it degrades the performance of the server.
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