Quick Answer: Which View Does Not Always Allow DML Operations Through The View?

Which is a virtual table that provides a window through which one can see data?

In SQL, a view is a virtual table based on the result-set of an SQL statement.

A view contains rows and columns, just like a real table.

The fields in a view are fields from one or more real tables in the database..

Can we delete data from materialized view?

You cannot delete rows from a read-only materialized view. If you delete rows from a writable materialized view, then the database removes the rows from the underlying container table. However, the deletions are overwritten at the next refresh operation.

Are views updated automatically?

A view is basically a stored query, it holds no data so no, it won’t get updated when the tables it’s built on are. However as soon as you reference the view the query it’s based on will run, so you will see the changes made to the base tables. Yes, a view is a SELECT query against underlying tables/views.

What are the restrictions of DML operations on views?

DML operations can be performed upon a table through view….Ø A Row can be removed from a view unless it contains:Group Function.A Group by Clause.The Rownum Pesudo column.The Distinct key word.The columns defined by expressions.

What are views describe different types of views?

There are two types of database views: dynamic views and static views. Dynamic views can contain data from one or two tables and automatically include all of the columns from the specified table or tables. Dynamic views are automatically updated when related objects or extended objects are created or changed.

Can we update data using view?

You can insert, update, and delete rows in a view, subject to the following limitations: If the view contains joins between multiple tables, you can only insert and update one table in the view, and you can’t delete rows. You can’t directly modify data in views based on union queries.

Which SQL statement is used to remove the view?

DROP VIEW statementUse the DROP VIEW statement to remove a view or an object view from the database.

Are views stored in database?

A view is a virtual table whose contents are defined by a query. Like a table, a view consists of a set of named columns and rows of data. Unless indexed, a view does not exist as a stored set of data values in a database.

Which command helps in redefining the view definition without dropping the existing view?

You can also use ALTER VIEW to define, modify, or drop view constraints. This statement does not change the definition of an existing view. To redefine a view, you must use CREATE VIEW with the OR REPLACE keywords.

Why do we use view in SQL?

Views are used for security purposes because they provide encapsulation of the name of the table. Data is in the virtual table, not stored permanently. Views display only selected data. We can also use Sql Join s in the Select statement in deriving the data for the view.

Can we delete from view in Oracle?

When you delete rows from an updatable view, Oracle Database deletes rows from the base table. You cannot delete rows from a read-only materialized view. If you delete rows from a writable materialized view, then the database removes the rows from the underlying container table.

What Cannot be done on a view?

What cannot be done on a view? Explanation: In MySQL, ‘Views’ act as virtual tables. It is not possible to create indexes on a view. However, they can be used for the views that are processed using the merge algorithm.

Why do we use views instead of tables?

Views can join and simplify multiple tables into a single virtual table. … Views can hide the complexity of data. Views take very little space to store; the database contains only the definition of a view, not a copy of all the data that it presents. Views can provide extra security, depending on the SQL engine used.

Which query will create the Cartesian product?

The SQL CROSS JOIN produces a result set which is the number of rows in the first table multiplied by the number of rows in the second table if no WHERE clause is used along with CROSS JOIN. This kind of result is called as Cartesian Product. If WHERE clause is used with CROSS JOIN, it functions like an INNER JOIN.

Can we do DML operations on view?

In simple view We create view on single base table That’s why we can perform all DML operations.it also called as Updatable view. But In case of Complex view We create view on multiple base tables that’s why we cannot perform DML operations It is ReadOnly View (Only Select Operation).

What is the advantage of view in SQL?

Views can provide advantages over tables: Views can represent a subset of the data contained in a table. Consequently, a view can limit the degree of exposure of the underlying tables to the outer world: a given user may have permission to query the view, while denied access to the rest of the base table.

Can we create view without table in Oracle?

A view can be created even if the defining query of the view cannot be executed. … For example, if a view refers to a non-existent table or an invalid column of an existing table or if the owner of the view does not have the required privileges, then the view can still be created and entered into the data dictionary.

What view means?

transitive verb. 1 : to look at attentively : scrutinize, observe view an exhibit. 2a : see, watch. b : to look on in a particular light : regard doesn’t view himself as a rebel. 3 : to survey or examine mentally : consider view all sides of a question.