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Yes, you can create a view within a view.
Yes, you can JOIN views with tables. You can use views just like tables in SELECTs. Special considerations apply in other operations.
The syntax for the CREATE VIEW Statement in Oracle/PLSQL is: CREATE VIEW view_name AS SELECT columns FROM tables [WHERE conditions]; view_name. The name of the Oracle VIEW that you wish to create.
Indexes can only be created on views which have the same owner as the referenced table or tables.
Nested views are bad. Instead of copying and pasting the code wherever you need it, or using a stored procedure (because for some reason you’re allergic to stored procedures), you decide to simplify your code and re-use that SELECT in the form of a database view. …
Nested views–views that are called by another view–invariably start off with the best of intentions. Theoretically, there’s nothing wrong with using a nested view as long as you’re aware of the performance implications. … But in practice, nested views create more problems than they solve.
The ORDER BY clause is not valid in views, inline functions, derived tables, and subqueries, unless either the TOP or OFFSET and FETCH clauses are also specified. When ORDER BY is used in these objects, the clause is used only to determine the rows returned by the TOP clause or OFFSET and FETCH clauses.
|Que.||Which operation are allowed in a join view:|
|d.||All of the mentioned|
|Answer:All of the mentioned|
A join is an SQL operation performed to establish a connection between two or more database tables based on matching columns, thereby creating a relationship between the tables. … The type of join a programmer uses determines which records the query selects.
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.
There is no ‘;with’ clause. Although you will often see developers add a semicolon before WITH as a kudge, the requirement is that the statement before the WITH (and some other newer statements) be terminated with a semicolon. There is no preceeding statement in your view so just omit the semicolon like Jeff’s example.
No, you cannot alter the query of a materialized view without dropping it. The CREATE MATERIALIZED VIEW syntax does not support that feature. The ALTER MATERIALIZED VIEW is used to modify an existing materialized view in one or more of the following ways: To change its storage characteristics.
Triggers may be created on views, as well as ordinary tables, by specifying INSTEAD OF in the CREATE TRIGGER statement. If one or more ON INSERT, ON DELETE or ON UPDATE triggers are defined on a view, then it is not an error to execute an INSERT, DELETE or UPDATE statement on the view, respectively.
Views make queries faster to write, but they don’t improve the underlying query performance. … In short, if an indexed view can satisfy a query, then under certain circumstances, this can drastically reduce the amount of work that SQL Server needs to do to return the required data, and so improve query performance.
The view is not “holding data”, it is holding a query. The query statement has constants in it that are turned into a result set that can be used by other queries.
re: Why Views are evil. Using Views in your query doesn’t make a trip to the D/B Server instead the View results are stored in the Cache. Hence Complex Queries such as Report Queries tend to run much faster when making joins with views than using tables.
You cannot pass parameters to SQL Server views. Cannot use an Order By clause with views without specifying FOR XML or TOP. Views cannot be created on Temporary Tables. You cannot associate rules and defaults with views.
Only its owner may destroy a table. … (CASCADE will remove a dependent view entirely, but in the foreign-key case it will only remove the foreign-key constraint, not the other table entirely.)
Views can be created from a single table, multiple tables or another view. To create a view, a user must have the appropriate system privilege according to the specific implementation.
Right-click on a view and select Modify (or Design in SQL Server 2008) then specify a sort order in the Criteria Pane and press Enter. Instead of indicating an error, SSMS will insert the ORDER BY in the view and will generate a TOP 100 PERCENT within the SELECT as well.
57) What is true about views among all the given below statements: View never references actual table for which it is created. View can’t use JOIN in it’s query. The performance of the view degrades if they are based on other views.
For SQL Server, CROSS JOIN and FULL OUTER JOIN are different. CROSS JOIN is simply Cartesian Product of two tables, irrespective of any filter criteria or any condition. FULL OUTER JOIN gives unique result set of LEFT OUTER JOIN and RIGHT OUTER JOIN of two tables.
Yes we can update view, if :- if view is created on a single table – if view contains the primary key field – if view contains all the not null fields of underlying tables – if view query doesn’t contain group by or any aggregated field.
Explanation: VIEW is a virtual table, through which a selective portion of the data from one or more tables can be seen. A view do not contain data of their own.
A top-level VIEW statement that you create using the VIEW statement is called a view (the Oracle CQL equivalent of a subquery). A join is a query that combines rows from two or more streams, views, or relations.
Difference between JOIN and INNER JOIN JOIN returns all rows from tables where the key record of one table is equal to the key records of another table. The INNER JOIN selects all rows from both participating tables as long as there is a match between the columns.
Inner joins combine records from two tables whenever there are matching values in a field common to both tables. You can use INNER JOIN with the Departments and Employees tables to select all the employees in each department.
There are 2 types of Views in SQL: Simple View and Complex View. Simple views can only contain a single base table.
Force View does forces the creation of a View even when the View will be invalid. NoForce Is the default. Code. CREATE FORCE VIEW.
FORCE keyword is used while creating a view, forcefully. This keyword is used to create a View even if the table does not exist.
- CREATE VIEW view_name AS.
- SELECT columns.
- FROM tables.
- WHERE conditions;
A common table expression (CTE) is a named temporary result set that exists within the scope of a single statement and that can be referred to later within that statement, possibly multiple times. The following discussion describes how to write statements that use CTEs.
- In Object Explorer, click the plus sign next to the database where your view is located and then click the plus sign next to the Views folder.
- Right-click on the view you wish to modify and select Design.
Materialized views are disc-stored views that can be refreshed. … You can’t insert data into a materialized view as you can with a table. To update the contents of a materialized view, you can execute a query to refresh it. This will re-execute the query used to create it.
Users cannot perform data manipulation language (DML) statements on read-only materialized views, but they can perform DML on updatable and writeable materialized views.
TRUNCATE MATERIALIZED VIEW command Examples Create a base table, add rows, and create a materialized view on that base table. CREATE OR REPLACE TABLE temp INSERT INTO temp SELECT seq8() FROM table(generator(rowcount=>20)) v; CREATE MATERIALIZED VIEW mv1.
To view database level triggers, Login to the server using SQL Server management studio and navigate to the database. Expand the database and navigate to Programmability -> Database Triggers. To view triggers at the server level, Login to Server using SSMS and navigate to Server Objects and then Triggers folder.
There are two kinds of DML triggers the FOR (or AFTER) trigger and the INSTEAD OF trigger, but the only one you can use with views are INSTEAD OF triggers. In contrary to the AFTER type which fires after an event, the INSTEAD OF trigger executes instead of the firing statement.
The INSTEAD OF clause is used for creating trigger on a view.