20 SQL Views Interview Questions and Answers

SQL views are a way of storing a query in the database so that it can be reused. Views can be used to simplify complex queries, to provide security by hiding certain columns or rows of data, or to provide an alternative to materialized views. In this article, we will discuss some common interview questions about SQL views so that you can be prepared for your next job interview.

SQL Views Interview Questions and Answers

Here are 20 commonly asked SQL Views interview questions and answers to prepare you for your interview:

1. What are views in SQL?

Views are a type of virtual table, which means that they are not actually stored as a separate table in the database, but are instead generated on the fly when needed. Views are often used to provide security, since they can be used to restrict access to certain parts of the database. They can also be used to simplify queries, by hiding complexity or aggregating data.

2. How do you create a view in SQL Server?

In SQL Server, you can create a view by using the CREATE VIEW statement. This statement allows you to specify the name of the view, the name of the table that the view will be based on, and the columns that will be included in the view. You can also specify any filters or conditions that should be applied to the data in the view.

3. How does the WITH CHECK OPTION clause work when creating a view?

The WITH CHECK OPTION clause ensures that any data modifications made to the view can be successfully checked against the underlying data in the table. This means that the view must be created with a SELECT statement that is guaranteed to return only data that is compatible with the data in the underlying table.

4. How do you update data through a view?

In SQL, a view is a virtual table based on the result-set of an SQL statement. A view 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. You can update data through a view, as long as the view is updatable. This means that the view must not have any of the following:

– Aggregate functions (SUM, COUNT, MIN, MAX, etc.)
– The DISTINCT keyword
– GROUP BY or HAVING clauses
– Joins
– Unions
– Subqueries

5. How do you insert data through a view?

You can’t insert data through a view unless the view is based on a single table and the view doesn’t have a WHERE clause.

6. Can you explain how the SCHEMABINDING option works with views?

The SCHEMABINDING option ensures that the view cannot be modified if any of the schema-bound objects it references are modified in a way that would affect the view definition. This option also allows you to create indexes on views.

7. Can you give me some examples of why we would want to use views?

Views can be used for a number of reasons. For example, they can be used to restrict access to certain data so that only authorized users can see it. Views can also be used to simplify complex queries by breaking them down into smaller, more manageable pieces. Additionally, views can be used to provide an alternative way of looking at the data in a database, which can be useful for different types of users.

8. When should I consider using a view instead of writing queries against base tables?

Views can be useful when you want to encapsulate a complex query or when you want to provide restricted access to data in a table. For example, if you have a table that contains sensitive information, you could create a view that only shows non-sensitive information. That way, users who only have access to the view will not be able to see the sensitive data.

9. Are there any restrictions on which columns can be used while creating a view?

There are no restrictions on which columns can be used while creating a view. However, all columns used in the view must come from the same table.

10. What happens if two users try to modify the same column at the same time through views?

If two users try to modify the same column at the same time through views, the database will throw an error.

11. Is it possible to write complex joins and other operations on a view?

Yes, it is possible to write complex joins and other operations on a view. However, it is important to keep in mind that the view itself is not a physical table, so the performance of these operations may not be as good as if they were performed on a physical table.

12. Why is it important to index views in SQL?

Indexing views is important because it can help improve the performance of queries that are run against the view. By indexing the view, you are essentially creating a shortcut that the query can use to more quickly find the data it is looking for. This can be especially helpful if the view is based on a large table or multiple tables.

13. Does a view always have to contain all rows from its underlying table?

No, a view does not always have to contain all rows from its underlying table. In fact, one of the main purposes of a view is to provide a way to select a subset of data from a table. For example, you might create a view that only contains rows with a certain status code, or that only contains rows from a certain date range.

14. Can you give me an example of where a join view might be useful?

A join view might be useful in a situation where you have data spread out across multiple tables and you want to be able to query that data as if it were all in one table. For example, if you have a customer table and an order table, you could create a join view that combines the two tables and allows you to query them as if they were one.

15. How can you determine what permissions different databases or database objects have been granted to specific users?

You can use the sp_helprotect system stored procedure to determine what permissions different databases or database objects have been granted to specific users.

16. Can you give me an example of how a materialized view might improve performance?

A materialized view is a type of SQL view that is stored on the database server. This can improve performance because the view does not need to be recreated each time it is accessed.

17. What is the difference between a global temporary view and a local temporary view?

Global temporary views are available to all sessions, while local temporary views are only available to the session in which they were created.

18. Do views automatically get dropped when the table they’re built on gets dropped? If no, then how do you drop them manually?

No, views do not automatically get dropped when the table they’re built on gets dropped. In order to drop a view, you will need to use the DROP VIEW command.

19. Is it possible to create a recursive view? If yes, then how?

Yes, it is possible to create a recursive view. In order to do so, you will need to use the WITH clause to specify the view as a recursive view.

20. Is it good practice to store data in a view?

While there are some benefits to storing data in a view (such as increased security and easier maintenance), it is generally not considered good practice. This is because views are typically less efficient than tables, and they can also be more difficult to work with.