In SQL, a view is a virtual table derived from the result of a query. It is not a physical table but rather a saved SQL statement that can be used as a convenient way to retrieve and manipulate data. Views offer several benefits, including simplifying complex queries, providing data security, and enhancing query performance. Here are some key points about SQL views:

1. Purpose: Views are primarily used to simplify queries and provide a logical layer of abstraction over the underlying tables. They allow you to create custom "virtual" tables that represent a specific subset of data or present data in a different format without modifying the underlying schema.

2. Definition: A view is defined by a SELECT statement that retrieves data from one or more tables, optionally applying filters, joins, or aggregations. Once defined, a view can be referenced in other queries, treated like a regular table, and used for data retrieval, modification, or even as a basis for creating other views.

3. Data Retrieval: Views act as stored queries. When you query a view, the database engine executes the underlying SELECT statement and returns the result set as if you had directly queried the source tables.

4. Data Modification: In many database systems, views can be updatable, allowing you to perform INSERT, UPDATE, and DELETE operations on the view. However, certain conditions must be met, such as having a unique key defined, following specific rules for updatable views, and ensuring that the modifications are propagated to the underlying tables.

5. Security: Views can be used to restrict access to sensitive data. By granting users access only to specific views and not the underlying tables, you can control what data they can see and manipulate, providing an additional layer of security.

6. Query Simplification: Views are particularly useful for encapsulating complex queries. Instead of writing the same complex query repeatedly, you can create a view and refer to it by name whenever you need the results.

7. Performance Optimization: Views can be utilized to optimize query performance. By predefining commonly used joins, aggregations, or complex calculations in a view, you can avoid repetitive computations and simplify the execution plan, potentially improving query performance.

8. Materialized Views: Some database systems support materialized views, which are precomputed and stored physically on disk. Materialized views are updated periodically or on-demand, providing improved performance for frequently executed queries at the expense of increased storage and potential data staleness.

9. View Dependencies: Views can depend on other views or tables, creating a hierarchical relationship. If a view that is referenced by other views or queries is modified, the dependent views may need to be updated or invalidated to ensure data consistency.

10. View Management: Views can be created, altered, or dropped using SQL statements, similar to tables. They can also be used in conjunction with other database objects like indexes, triggers, or constraints.

Views offer a powerful tool for data abstraction, security, and query optimization in SQL databases. They enable developers to simplify complex queries, enhance data access control, and improve overall performance. However, it's important to consider the performance implications, maintainability, and potential dependencies when designing and utilizing views in your database schema.