In the context of databases, a "View" refers to a virtual or logical table that is derived from one or more base tables, often referred to as underlying tables. Unlike a standard table, a view doesn't physically store the data, but rather it represents a predefined query on one or more underlying tables, essentially storing the SQL statement that defines it.
Definition:
View - A view is a stored query that operates on underlying tables to present data as if it were a single, unified table structure. It can encapsulate complex queries, joining data from multiple tables, filtering it, sorting it, and presenting it in a specific structure or order. Views can be thought of as a lens through which you can see the data, tailored to specific needs.
Details:
Virtual Nature: Since a view only contains a query and not the actual data, it takes up minimal space in the database and always presents the latest data from the underlying tables. Changes to the data in the underlying tables are automatically reflected in the view.
Simplification: Views can abstract the complexity of underlying database structure. They can join several tables and apply transformations to provide users with the data in the required format. This simplifies the interaction for end-users who can treat the view as a regular table.
Security: By restricting access to specific columns or rows in the underlying tables, views can act as a security mechanism. Users who have access to a view but not the underlying tables can only see the data that is presented by the view.
Read-Only or Updatable: Many views are read-only, meaning that you cannot modify the data through the view. Some databases also support updatable views, allowing data modification, but this typically comes with restrictions and depends on the complexity of the view.
Performance Consideration: As views execute the stored query every time they are accessed, complex views with joins across multiple large tables may introduce performance overhead.
Schema Stability: Views can provide stability to applications even if the underlying schema changes. As long as the view can still execute the query with the new schema, applications interacting with the view do not need to be modified.
Materialized Views: Some databases support materialized views, where the result of the view's query is physically stored and periodically updated. This offers performance benefits for complex queries at the cost of additional storage and potential staleness between updates.
A view in a database context is a powerful abstraction tool, offering a flexible way to access and manipulate underlying data without directly interacting with the physical tables. It aids in simplifying queries, enforcing security, and providing a stable interface to application developers. It is an essential concept in modern database design and utilization.
