Views serve multiple important purposes in database management

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A view in a database is a virtual table that is derived from one or more underlying base tables or other views. Unlike a base table, a view does not store data physically. Instead, it stores a SQL query that dynamically generates the result set when the view is accessed. Views provide a way to present data in a specific format or subset without duplicating the data.

Purpose of Views
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Simplify Complex Queries: Views allow users to encapsulate complex joins and filters within a single virtual table. This simplifies query writing for end-users who can interact with the view instead of writing complicated SQL each time.

Data Security: Views can restrict access to sensitive data by exposing only specific columns or rows of the underlying tables. This allows database administrators to control user permissions at a more granular level.

Data Abstraction: Views provide a layer of abstraction between the physical data storage and how data is presented. This means underlying tables can be changed without affecting how users query data through views, as long as the view definition remains valid.

Reusability and Consistency: By defining business logic or common queries as views, organizations promote reusability and maintain consistency in data access.

Types of Views
Simple Views: These are based on a single table and do iceland phone number list not contain functions, groupings, or joins. Simple views can often be updatable, allowing INSERT, UPDATE, or DELETE operations on the view to affect the underlying table.

Complex Views: These involve multiple tables, joins, aggregations, or calculations. Complex views are typically read-only, as changes to the view cannot always be mapped back to the underlying tables reliably.

How Views Work
When a view is queried, the database engine substitutes the view’s SQL query into the user's query, effectively running a combined query against the underlying tables. Since views do not store data, they always reflect the current data in the base tables.

Materialized Views
A special type of view called a materialized view physically stores the query result and must be refreshed periodically. Materialized views improve performance for expensive queries by avoiding recalculation each time the view is accessed but require additional storage and maintenance.

Advantages and Limitations
Advantages:

Improve security by restricting data access

Simplify user queries and provide consistent data representation

Help in database abstraction and maintenance

Limitations:

Some views may be non-updatable

Performance can be slower for complex views since they compute results on demand unless materialized

In summary, views are a powerful database feature that enables flexible, secure, and simplified access to data without data duplication, enhancing both user experience and database management.