FORCE View

In Oracle, the FORCE option for views is a feature used to force the creation of a view even if it is not updatable. This option allows the creation of views where the standard conditions for updatability are not met but still need to be created.

The FORCE option is typically used when you want to ensure that the view can be created in cases where the view might otherwise be non-updatable (for example, because of certain complex conditions or aggregations). However, it's important to note that FORCE views may not always be able to perform data modifications (insert, update, delete) due to their complexity.

1. What is the FORCE Option in Oracle?

The FORCE option is used when creating a view to override certain restrictions that would otherwise prevent the view from being created in Oracle. By using FORCE, Oracle allows the creation of the view, even if it includes features that would normally make it non-updatable, like:

• Aggregation (SUM(), AVG(), etc.)
• Joins between multiple tables
• Grouped data (GROUP BY)
• Subqueries in the FROM clause or WHERE clause

The FORCE option forces Oracle to create the view but does not necessarily make it updatable. This means that the view can still be queried, but data modification operations (e.g., INSERT, UPDATE, DELETE) may not be allowed.

2. Syntax for Creating a Force View

To create a view with the FORCE option, the syntax is as follows:

CREATE FORCE VIEW view_name AS

SELECT column1, column2, ...

FROM table_name

WHERE condition;

• The FORCE keyword is placed before the VIEW keyword in the CREATE VIEW statement.
• If Oracle encounters any issues that would normally prevent the view from being created (such as a non-updatable query), the FORCE option will bypass those checks and allow the creation of the view.

3. When to Use the FORCE Option

You would use the FORCE option in situations where:

• Complex Views: You want to create a view that involves complex queries, joins, aggregations, or other operations that Oracle normally considers non-updatable.
• Maintaining Consistency: You need a view that still provides useful information, even though direct data modification might not be possible through the view.
• Enforcing a View's Existence: You want to enforce the existence of a view despite its complexity or the fact that it is non-updatable.
• Cross-Platform Migration: When migrating schemas from other databases to Oracle and you want to preserve existing view structures, even if they are non-updatable.

4. Example of a FORCE View

Let's say you have a view that involves aggregation, making it non-updatable. You can force the creation of the view with the FORCE keyword:

CREATE FORCE VIEW department_salary AS

SELECT department_id, SUM(salary) AS total_salary

FROM employees

GROUP BY department_id;

In this example:

• The view aggregates salaries by department.
• Normally, this would be a non-updatable view because it involves aggregation, but using the FORCE option, Oracle allows its creation.
• However, since the view involves an aggregation function (SUM()), you cannot modify the data directly via this view (i.e., INSERT, UPDATE, DELETE would not be allowed).

5. How Does FORCE View Affect Data Modifications?

Even though you can create the view with the FORCE keyword, this does not guarantee that you will be able to perform data modifications (insert, update, or delete) through the view.

• Data Modifications: If the view involves complex operations like joins or aggregations, you may still not be able to perform data-modifying operations through it. The FORCE option does not make the view inherently updatable.
• Querying: You can still query the view using SELECT statements, regardless of the complexity, as long as the view can be logically derived from the underlying tables.

6. Restrictions of Using FORCE View

The FORCE option can override some restrictions for view creation, but there are some important limitations:

• Not Always Updatable: Even with FORCE, the view might not be updatable if it involves complex operations like joins, aggregations, DISTINCT, or subqueries. You cannot modify the underlying data directly through the view.
• Complex Queries: If the view’s underlying query involves aggregation, joins, or complex expressions, Oracle may still block modification operations (e.g., UPDATE, DELETE, INSERT) even though the view is created using FORCE.
• Performance Overhead: Using complex views, especially those created with FORCE, could impact query performance, as Oracle might need to perform additional work to handle the view's logic.

7. How to Make a FORCE View Updatable

If you create a FORCE view that you want to be updatable, you must simplify the view's underlying query:

• Remove Joins: Create views based on a single table when possible.
• Avoid Aggregations: Eliminate GROUP BY, SUM(), AVG(), and other aggregation functions.
• Simplify the WHERE Clause: Ensure the WHERE clause is straightforward and does not involve subqueries or complex expressions.

8. Example of Creating an Updatable View with FORCE

To create a FORCE view that is updatable, you can simplify the query. For example:

CREATE FORCE VIEW employee_details AS

SELECT employee_id, first_name, last_name, department_id

FROM employees;

This view:

• Involves only a single table (employees).
• Has no aggregation, joins, or grouping.
• Is updatable, and you can perform INSERT, UPDATE, and DELETE operations via the view.

9. Checking If a View is Updatable or Read-Only

Oracle does not provide a direct method to check whether a view created with FORCE is updatable or not, but you can test it by attempting to perform data-modifying operations (e.g., INSERT, UPDATE, DELETE).

Alternatively, you can query the view metadata using the ALL_VIEWS or USER_VIEWS views to inspect the view's underlying structure, but checking whether a view is actually updatable requires a practical test.

10. Dropping a FORCE View

To drop a FORCE view, use the DROP VIEW statement, just like any other view:

DROP VIEW department_salary;

This will remove the view from the database, and it will not affect the underlying tables or data.

11. Benefits of Using FORCE Views

• Flexibility: Allows you to create complex views that would normally be blocked by Oracle’s standard updatability rules.
• Enforced View Creation: Ensures that the view is created even if it would normally be non-updatable due to complexity.
• Convenience: Allows you to maintain complex queries in a centralized location, which can be useful for reporting or other purposes.

12. Drawbacks of Using FORCE Views

• Non-Updatable: A FORCE view is likely to be non-updatable, meaning you cannot perform data-modifying operations through it.
• Performance: Complex views created with the FORCE option might affect query performance, especially if they involve joins, aggregations, or subqueries.
• Data Integrity: Since data modifications through a FORCE view are restricted, you need to carefully design your application to ensure that users can still modify the data through other means.

 

Conclusion

The FORCE option in Oracle is useful for forcing the creation of complex views that would otherwise be non-updatable due to certain operations like joins, aggregations, and subqueries. While this option provides flexibility in creating views, it doesn't guarantee that data can be modified via the view. It is important to consider the complexity of the view and how it may affect data modification capabilities. If you need a view to be updatable, it’s best to simplify the underlying query or consider alternative design strategies.