Frequent question: How are views implemented in SQL?

How are views implemented?

Database views are created using the CREATE VIEW statement. 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.

How do views work in SQL?

A VIEW in SQL Server is like a virtual table that contains data from one or multiple tables. It does not hold any data and does not exist physically in the database. Similar to a SQL table, the view name should be unique in a database. It contains a set of predefined SQL queries to fetch data from the database.

How are SQL views stored?

Views are a special version of tables in SQL. … The view is a query stored in the data dictionary, on which the user can query just like they do on tables. It does not use the physical memory, only the query is stored in the data dictionary. It is computed dynamically, whenever the user performs any query on it.

How are views created in SQL Server?

SQL Server CREATE VIEW

  1. First, specify the name of the view after the CREATE VIEW keywords. The schema_name is the name of the schema to which the view belongs.
  2. Second, specify a SELECT statement ( select_statement ) that defines the view after the AS keyword. The SELECT statement can refer to one or more tables.
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Can a trigger be created on a view?

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.

Can we insert and delete rows into a view?

Yes, possible to insert,update and delete to view. view is a virtual table. Same Perform as insert,update,delete query.. A view can be defined as a virtual table or a stored query and the data accessible through a view is not stored in the database as a distinct object.

How many types of views are there?

There are total four types of views, based on the way in which the view is implemented and the methods that are permitted for accessing the view data. They are – Database Views, Projection Views, Maintenance Views, and Helps Views,.

How do you write a trigger?

create trigger [trigger_name]: Creates or replaces an existing trigger with the trigger_name. [before | after]: This specifies when the trigger will be executed. {insert | update | delete}: This specifies the DML operation. on [table_name]: This specifies the name of the table associated with the trigger.

How do you display in SQL?

The DISPLAY command must be placed immediately after the query statement on which you want it to take effect. For example: SELECT pno, pname FROM part WHERE color=’BLUE’; DISPLAY; When the system encounters this DISPLAY command, it displays the Result window containing the part number and name for all blue parts.

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Are SQL views permanent?

View is a simple SQL statement that is stored in database schema (INFORMATION_SCHEMA. Views). So when ever we call the view the SQL statement gets executed and return the rows from main physical table.

Does a SQL view take up space?

To create a view, you use the SQL syntax: … For this reason, the view does not take up any disk space for data storage, and it does not create any redundant copies of data that is already stored in the tables that it references (which are sometimes called the base tables of the view).

Are views stored in a 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.

What is difference between stored procedure and function?

The function must return a value but in Stored Procedure it is optional. Even a procedure can return zero or n values. Functions can have only input parameters for it whereas Procedures can have input or output parameters. Functions can be called from Procedure whereas Procedures cannot be called from a Function.