In a relational database, a view is a virtual table that is derived from one or more underlying tables. Unlike a physical table, a view does not store any data of its own; instead, it simply presents a customized view of the data that is stored in the underlying tables. Views can be used to simplify the querying of data, to present data in a specific format, or to restrict access to certain data.
When you create a view in SQL, you define a SELECT statement that specifies the columns and rows that should be included in the view. For example, you might create a view that only includes data from certain columns in a table, or that filters out certain rows based on specific criteria. Once the view is created, it can be queried just like a physical table, using the same SQL constructs and syntax.
There are several advantages to using views in a database:
Simplified querying - By defining a view that presents the data in a specific way, you can simplify the process of querying the database. Instead of having to write complex SQL statements that join multiple tables and apply filters, you can simply query the view using a much simpler SELECT statement.
Data security - Views can be used to restrict access to sensitive data in a database. For example, you might create a view that only includes certain columns of a table, or that filters out certain rows based on specific criteria. By granting users access to the view instead of the underlying table, you can control what data they are able to see.
Data consistency - Views can be used to ensure that data is presented in a consistent way across different applications or users. By defining a view that presents the data in a specific format, you can ensure that all users see the same data in the same way.
Performance optimization - Views can be used to optimize the performance of complex queries by precomputing the results of a query and storing them in a view. This can significantly reduce the time required to execute the query, especially if the underlying tables are very large or complex.
In summary, views are a powerful tool for simplifying the querying of data, controlling access to sensitive data, ensuring data consistency, and optimizing performance in a relational database. By defining views that present the data in a specific way, you can make it easier for users to interact with the database and ensure that the data is used in a consistent and secure manner.
