Schema Management
SQL Views
Creating and Using SQL Views
Views simplify queries, with materialized views for stored results.
What are SQL Views?
SQL Views are virtual tables representing the result of a database query. They provide an abstraction layer and simplify complex queries by encapsulating them within a single, reusable entity. Unlike tables, views do not store data themselves but present data stored in other tables.
Creating a Basic SQL View
To create a view, you use the CREATE VIEW statement followed by a query that defines the view. Once created, you can query the view as though it were a regular table.
Advantages of Using Views
- Simplified Queries: Complex SQL queries can be encapsulated into views, making them easier to manage and reuse.
- Security: Views can restrict access to specific rows or columns, enhancing data security.
- Consistency: By using views, you ensure consistent query results across different parts of an application.
Updating Data Through Views
While you can SELECT from a view like a table, updating data through a view has certain restrictions. Views are generally read-only unless they adhere to specific conditions, such as having a one-to-one mapping with a base table and not including aggregate functions.
In this example, the UPDATE statement will only work if employee_view meets the conditions allowing updates.
Materialized Views
Unlike regular views, materialized views store the result set of a query physically. This can enhance performance for complex queries, especially when dealing with large datasets. However, they require periodic refreshing to ensure data consistency with the base tables.
Materialized views can significantly reduce query time for aggregated data.
Maintaining Materialized Views
To keep materialized views up-to-date, they must be refreshed. This can be done manually or automatically at specified intervals.
Consider your system's performance needs and data update frequency when deciding how often to refresh a materialized view.
