Are views updatable in Oracle?
Are views updatable in Oracle?
Views in Oracle may be updateable under specific conditions. It can be tricky, and usually is not advisable. An updatable view is one you can use to insert, update, or delete base table rows. You can create a view to be inherently updatable, or you can create an INSTEAD OF trigger on any view to make it updatable.
Which views are updatable?
An updatable view is a special case of a deletable view. A deletable view becomes an updatable view when at least one of its columns is updatable. A column of a view is updatable when all of the following rules are true: The view is deletable.
Under what circumstances is a view said to be updatable in Oracle?
A view behaves like a table because you can query data from it. However, you cannot always manipulate data via views. A view is updatable if the statement against the view can be translated into the corresponding statement against the underlying table.
What is materialized view in Oracle?
A materialized view is a database object that contains the results of a query. You can select data from a materialized view as you would from a table or view. In replication environments, the materialized views commonly created are primary key, rowid, object, and subquery materialized views.
Can you create an index on updatable views?
Indexes can only be created on views which have the same owner as the referenced table or tables. This is also called an intact ownership-chain between the view and the table(s). Typically, when table and view reside within the same schema, the same schema-owner applies to all objects within the schema.
What is updatable view in SQL Server?
Updatable Views Any modifications, including UPDATE, INSERT, and DELETE statements, must reference columns from only one base table. The columns being modified in the view must directly reference the underlying data in the table columns.
Which statement is not valid for an updatable view?
If a view is not updatable, statements such UPDATE , DELETE , and INSERT are illegal and are rejected.
Why materialized views are used?
Materialized views are basically used to increase query performance since it contains results of a query. They should be used for reporting instead of a table for a faster execution.
What are the differences between views and materialized views?
The basic difference between View and Materialized View is that Views are not stored physically on the disk. However, Materialized View is a physical copy, picture or snapshot of the base table. A view is always updated as the query creating View executes each time the View is used.
Do indexes work on views?
1 Answer. A view is just a “saved query”. The indexes on the base table are still used whenever you access the view. You don’t need to use an indexed view, unless the view contains an expensive logic (aggregations or joins) that you don’t want to perform each time you query the view.
How do I create an updatable view?
However, to create an updatable view, the SELECT statement that defines the view must not contain any of the following elements:
- Aggregate functions such as MIN, MAX, SUM, AVG, and COUNT.
- DISTINCT.
- GROUP BY clause.
- HAVING clause.
- UNION or UNION ALL clause.
- Left join or outer join.
What is view table in Oracle?
In Oracle, view is a virtual table that does not physically exist. It is stored in Oracle data dictionary and do not store any data. It can be executed when called. A view is created by a query joining one or more tables.
What is an UPDATE statement in Oracle?
The Oracle UPDATE statement is used to update existing records in a table in an Oracle database. There are 2 syntaxes for an update query in Oracle depending on whether you are performing a traditional update or updating one table with data from another table.
What is the view in Oracle?
A View in Oracle and in other database systems is simply the representation of a SQL statement that is stored in memory so that it can easily be re-used.
What are external tables in Oracle?
The Oracle external tables feature allows us to access data in external sources as if it is a table in the database. External tables are read-only. No data manipulation language (DML) operations is allowed on an external table. An external table does not describe any data that is stored in the database.
