Exactly what is a view in Oracle?
A View in Oracle as well as in other database systems is just the representation of the SQL statement that's saved in memory to ensure that it may be easily re-used. For instance, as we frequently problem the next query
SELECT customerid, customername FROM customers WHERE countryid='US';
To produce a view make use of the CREATE VIEW command as observed in this situation
CREATE VIEW view_uscustomers AS SELECT customerid, customername FROM customers WHERE countryid='US';
This command produces a brand new view known as view_uscustomers. Observe that this command doesn't lead to anything being really saved within the database whatsoever aside from an information dictionary entry that defines this view. Which means that each time you query this view, Oracle needs to get out there and execute the vista and query the database data. We are able to query the vista such as this:
SELECT * FROM view_uscustomers WHERE customerid BETWEEN 100 AND 200;
And Oracle will transform the query into this:
SELECT * FROM (select customerid, customername from customers WHERE countryid='US') WHERE customerid BETWEEN 100 AND 200
Advantages of choosing Sights
- Commonality of code getting used. Since a view is dependant on one common group of SQL, which means that when it's known as it’s not as likely to want parsing.
- Security. Sights have lengthy been accustomed to hide the tables that really retain the data you're querying. Also, sights may be used to restrict the posts that the given user can access.
- Predicate pushing
You'll find advanced subjects in the following paragraphs about "How to produce and Manage Sights in Oracle."
If you want the thought of sights but they are concerned about performance you will get get Oracle to produce a cached table representing the vista which oracle keeps current.
See materialized sights
A view is really a virtual table, which supplies use of a subset of column from a number of table. A view can derive its data from a number of table. An creation of query could be saved like a view. View behave like small a table but it doesn't physically take any space. View is nice method to present data particularly customers from being able to access the table directly. A view in oracle is certainly not but a saved sql scripts. Sights itself contain no data.
A view is just any Choose query that's been given a title and held in the database. Because of this, a view may also be known as a named query or perhaps a saved query. To produce a view, you apply the SQL syntax: CREATE OR REPLACE VIEW AS Choose