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Understanding SQL Views

Understanding SQL Views

In the world of SQL (Structured Query Language), a "view" is a virtual table based on the result-set of an SQL statement. It contains rows and columns, just like a real table. The fields in a view are fields from one or more real tables in the database.

What is a View?​

A View is essentially a saved SQL query or a virtual table, which is stored in the database. The database does not store the data in the view, but rather the SQL statement that creates the view. This SQL statement is run every time the view is referenced in a query.

Why Use Views?​

Views are used for various reasons, some of which include:

  • Security: You can grant a user access to specific data and restrict data that user does not need to see.
  • Simplicity: A view can simplify the complexity of a query because it can encapsulate join statements. Instead of writing a complex query with joins, you can store the SQL as a view and then write simpler queries against the view.
  • Consistency: You can achieve data consistency. If multiple people are writing reports against the same data, they can use the same view rather than each person writing their own version of the query.

Creating a View​

To create a view, you use the CREATE VIEW statement followed by the view name, as, and the SELECT statement. The syntax is as follows:

CREATE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

The CREATE VIEW statement creates a new view in the database. You need to specify the view name after the CREATE VIEW clause and the underlying SELECT statement after the AS keyword.

Updating a View​

You can update a view by using the CREATE OR REPLACE VIEW statement. The syntax is as follows:

CREATE OR REPLACE VIEW view_name AS
SELECT column1, column2, ...
FROM table_name
WHERE condition;

The CREATE OR REPLACE VIEW statement either creates a new view or replaces an existing one if it already exists.

Deleting a View​

To delete a view, you use the DROP VIEW statement followed by the name of the view you want to delete. The syntax is as follows:

DROP VIEW view_name;

The DROP VIEW statement deletes the specified view from the database.

Conclusion​

In summary, a view is a powerful tool in SQL that allows you to simplify complex queries, enhance data security, and maintain data consistency. It should be noted that views are not physically present, and they take less space to store, as they are just the SQL statement and not the result set. It’s also worth mentioning that views always show the latest data because the database engine recreates the data every time a view is queried.