Creating Views in Oracle SQL

Key Concepts

Creating views in Oracle SQL involves defining a virtual table based on the result of a SQL query. Views do not store data but provide a way to simplify complex queries, control access to data, and present data in a more user-friendly format. Understanding the following key concepts is essential for effectively creating and using views:

1. CREATE VIEW Statement

The CREATE VIEW statement is used to create a new view. It specifies the view name and the query that defines the view. The view is then treated as a virtual table that can be queried just like a regular table.

2. Simplifying Complex Queries

Views can simplify complex queries by encapsulating the logic in a single object. This allows users to query the view without needing to understand the underlying complexity of the query.

3. Data Security

Views can be used to control access to data by exposing only specific columns or rows. This helps in maintaining data security and privacy by limiting what users can see and modify.

4. Data Abstraction

Views provide a level of abstraction by hiding the underlying table structure. This can be useful when the underlying tables are subject to frequent changes, as the view can remain consistent while the tables evolve.

5. Materialized Views

Materialized views are a special type of view that stores the result of the query physically. This can improve query performance for complex queries that are frequently executed, as the data is precomputed and stored.

Detailed Explanation

1. CREATE VIEW Statement

The basic syntax for the CREATE VIEW statement is:


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

Example: Creating a view named "EmployeeDetails" that selects specific columns from the "Employees" table:


CREATE VIEW EmployeeDetails AS
SELECT EmployeeID, FirstName, LastName, HireDate
FROM Employees;

2. Simplifying Complex Queries

Views can encapsulate complex queries, making them easier to use. For example, a view can combine data from multiple tables, perform calculations, or filter data based on specific criteria.

Example: Creating a view that combines data from the "Employees" and "Departments" tables:


CREATE VIEW EmployeeDepartment AS
SELECT e.EmployeeID, e.FirstName, e.LastName, d.DepartmentName
FROM Employees e
JOIN Departments d ON e.DepartmentID = d.DepartmentID;

3. Data Security

Views can be used to restrict access to sensitive data. For example, a view can be created to expose only non-sensitive columns, ensuring that users cannot access confidential information.

Example: Creating a view that exposes only the "EmployeeID", "FirstName", and "LastName" columns:


CREATE VIEW PublicEmployeeInfo AS
SELECT EmployeeID, FirstName, LastName
FROM Employees;

4. Data Abstraction

Views provide a layer of abstraction, allowing users to work with a simplified interface. This is particularly useful when the underlying tables have complex structures or are subject to frequent changes.

Example: Creating a view that abstracts the underlying table structure:


CREATE VIEW EmployeeSummary AS
SELECT EmployeeID, FirstName || ' ' || LastName AS FullName, HireDate
FROM Employees;

5. Materialized Views

Materialized views store the result of the query physically, improving performance for complex queries. They are particularly useful for queries that are executed frequently and involve large datasets.

Example: Creating a materialized view that stores the result of a complex query:


CREATE MATERIALIZED VIEW EmployeeSales AS
SELECT e.EmployeeID, e.FirstName, e.LastName, SUM(s.SalesAmount) AS TotalSales
FROM Employees e
JOIN Sales s ON e.EmployeeID = s.EmployeeID
GROUP BY e.EmployeeID, e.FirstName, e.LastName;

Understanding and mastering these concepts is essential for effectively creating and using views in Oracle SQL. By simplifying complex queries, controlling access to data, providing data abstraction, and leveraging materialized views, you can optimize your database design and improve query performance.