Simple View FAQS

 1. What is the difference between a simple view and a complex view?

• A simple view is based on a single table and does not involve complex operations like joins, subqueries, or aggregations.
• A complex view may involve multiple tables, joins, subqueries, or aggregation operations (e.g., GROUP BY), making it more intricate than a simple view.

2. Can a simple view be created with a JOIN clause?

No, a simple view cannot include a JOIN clause. It can only pull data from a single table. If you need to join multiple tables, you would need a complex view.

3. Can I use a simple view to update the underlying data?

Yes, but only if the view is based on a single table, and the columns involved are directly tied to the underlying table's columns without any transformations. You cannot update a simple view that includes expressions, DISTINCT, or aggregate functions.

4. What happens if I try to delete a row from a simple view?

You can delete rows from a simple view if it is based on a single table and the view does not contain any derived or aggregated data. Deleting a row from the view will remove it from the underlying table.

5. Can a simple view have a GROUP BY clause?

No, simple views cannot have a GROUP BY clause. This is reserved for more complex views that need to aggregate data from the underlying table.

6. Can I create a view that includes DISTINCT?

No, simple views cannot use DISTINCT because it may make the underlying data non-updatable. If you need a distinct result, consider using a more complex view.

7. Can I drop a view and how?

Yes, you can drop a view with the DROP VIEW statement. Example:

DROP VIEW view_name;

This will remove the view from the database but will not affect the underlying table or its data.

8. Can a simple view reference multiple columns from the same table?

Yes, a simple view can reference multiple columns from a single table. For example:

CREATE VIEW employee_view AS

SELECT employee_id, first_name, last_name, salary

FROM employees;

This view references several columns from the employees table.

9. Can I create a view based on a WHERE clause?

Yes, you can apply a WHERE clause to filter the data in a simple view. For example:

CREATE VIEW high_salary_employees AS

SELECT employee_id, first_name, last_name, salary

FROM employees

WHERE salary > 50000;

This view will return only employees with a salary greater than 50,000.

10. Is there a performance impact when using views?

• Since views are virtual (they don’t store data), querying a simple view has no direct storage impact. However, depending on the complexity of the underlying query or the size of the underlying table, performance can be affected.
• Simple views are generally faster than complex views because they don’t involve joins or aggregation.

11. Can a simple view be used in INSERT, UPDATE, or DELETE operations?

• INSERT: You can insert data into a simple view if the view contains updatable columns that directly map to the underlying table.
• UPDATE: You can update the data through a simple view as long as the view directly references columns that are updatable.
• DELETE: You can delete rows via a simple view, provided it points to a single table and contains only directly updatable columns.

12. Can I grant access to a view instead of a table?

Yes, you can grant access to a view rather than directly to the underlying table. This is often used for security purposes, where you limit access to certain columns or rows while hiding the complexity of the underlying data.

Example:

GRANT SELECT ON employee_view TO user_name;

13. Can I use a simple view in a JOIN with other tables?

While a simple view cannot contain a JOIN, you can use a simple view in a JOIN with other tables in your queries. For example:

SELECT e.first_name, e.last_name, d.department_name

FROM employee_view e

JOIN departments d ON e.department_id = d.department_id;

Here, employee_view is a simple view, but it’s being used in a join with the departments table.

14. What happens if I try to use a simple view with a GROUP BY clause?

You will get an error because simple views cannot use GROUP BY. If you need to perform aggregation, you must either modify the view to be more complex or handle aggregation in the query itself.

15. Can I rename a simple view?

No, you cannot directly rename a view in Oracle. To rename a view, you must drop the existing view and create a new one with the desired name.

DROP VIEW old_view_name;

CREATE VIEW new_view_name AS SELECT * FROM old_view_name;

16. Is it possible to create a view without defining the columns?

Yes, you can create a view without explicitly specifying column names in the CREATE VIEW statement. The column names will be taken from the query itself. For example:

CREATE VIEW employee_view AS

SELECT employee_id, first_name, last_name, salary FROM employees;

The view will inherit the column names from the SELECT query.