20 Database Index Interview Questions and Answers

Database indexing is a process that helps speed up the retrieval of data from a database. When you interview for a position that involves working with databases, the interviewer may ask you questions about indexing. Knowing how to answer these questions can help you demonstrate your knowledge and skills, and increase your chances of getting the job. In this article, we review some common questions about database indexing and how to answer them.

Database Index Interview Questions and Answers

Here are 20 commonly asked Database Index interview questions and answers to prepare you for your interview:

1. What are indexes in database management systems?

Indexes are used in database management systems to speed up the retrieval of data from the database. Indexes work by creating a copy of the data in the database that is sorted in a specific order. When a query is made for data from the database, the index can be used to quickly locate the desired data. Indexes can be created on one or more columns in a database table.

2. Can you explain how to create an index on a specific column of a table in Oracle?

In order to create an index on a specific column of a table in Oracle, you will need to use the CREATE INDEX statement. This statement will allow you to specify the name of the index, the name of the table, and the name of the column that you want to index.

3. How do you find out if there’s already an index defined on a particular column of a table in SQL Server?

You can use the sp_helpindex stored procedure to find out if there is already an index defined on a particular column of a table in SQL Server.

4. Is it possible to compare the performance of different types of indexes in MySQL? If yes, then how?

Yes, it is possible to compare the performance of different types of indexes in MySQL. You can do this by using the EXPLAIN command. This will show you how the MySQL optimizer is using the indexes to execute a query.

5. What are some of the advantages and disadvantages of using indexes?

Indexes can be very helpful in speeding up the performance of a database by allowing quick access to specific data. However, indexes can also slow down the performance of a database if they are not used correctly, or if there are too many of them. Additionally, indexes take up space in the database, so they should be used judiciously.

6. Can you give me some examples of where indexes can be used effectively?

Indexes can be used to speed up the performance of a database by allowing quick access to data that would otherwise be difficult to retrieve. For example, if you have a large database of customer information, you could use an index to quickly find all customers from a particular state or zip code. Indexes can also be used to enforce uniqueness constraints on data, such as ensuring that there are no duplicate customer records.

7. What is your opinion on building indexes on large tables? Do you think its useful or not?

There is no one-size-fits-all answer to this question, as it depends on the specific situation. In general, though, building indexes on large tables can be useful in order to improve query performance. If the table is frequently accessed and the queries are complex, then an index can help speed up the process. However, if the table is not accessed often or the queries are relatively simple, then an index may not be necessary.

8. What is the main difference between primary keys and unique indexes?

A primary key is a type of unique index that is used to identify a record in a database table. A unique index is used to enforce the uniqueness of the values in a column or set of columns.

9. How do you determine the type of indexing required for certain columns based on the type of data they hold?

The type of indexing required for certain columns is based on the type of data they hold. For example, if you have a column that holds numerical data, you would use a numeric index. If you have a column that holds text data, you would use a text index.

10. Why do you think clustered indexes have become less popular over time?

I think that the main reason for this is that clustered indexes tend to require more maintenance than non-clustered indexes, and as databases have become more complex, the overhead of maintaining a clustered index has become less feasible. Additionally, newer database management systems have been able to provide similar performance benefits to clustered indexes without the same maintenance requirements, making them a more attractive option.

11. What does the fill factor setting control in SQL Server?

The fill factor setting in SQL Server controls how much empty space is left in each index page. A lower fill factor will result in more empty space, which can help to improve performance when inserting new data into the index. However, a lower fill factor can also cause the index to take up more space on the disk.

12. Are there any situations when one should avoid creating indexes?

There are a few reasons why you might not want to create an index on a database table. The first is if the table is small enough that a full table scan would be more efficient. The second is if the table is going to be updated very frequently, as indexes need to be updated as well, which can cause performance issues. Finally, if the query you are trying to run is very complex, an index might not be able to help.

13. Are there any tools available that can help us identify which indexes need to be created on a given table?

There are a few different tools that can help with this, including the Database Index Tuning Wizard in SQL Server Management Studio and the Index Tuning Wizard in Oracle.

14. When would you want to build an index on a column with duplicate values?

In general, you would want to build an index on a column with duplicate values in order to improve query performance. An index can help the database to more quickly locate the desired data, which can be especially helpful if the column in question is frequently queried.

15. What are the best practices when it comes to defining indexes?

There are a few best practices to keep in mind when defining indexes:
1. Make sure that the columns you index are actually being used in queries – there’s no point in indexing a column that’s never referenced.
2. Avoid indexing too many columns – every index you create will slightly slow down write operations on the table, so only index the columns that will provide the biggest performance boost.
3. Be aware of the tradeoff between index size and performance – an index that covers more columns will be larger and take up more space, but it will also be faster. Choose the right balance for your needs.

16. In what case(s) would you prefer to use a non-clustered index instead of a clustered index?

There are a couple reasons you might want to use a non-clustered index instead of a clustered index. One reason is if you have a lot of reads but not many writes to the database – in this case, a non-clustered index can be more efficient because it doesn’t have to be updated as often as a clustered index. Another reason is if the data in the table is already in the order you want it, so there’s no need to reorder it when you create the index.

17. What is the purpose of an index in MongoDB?

Indexes are used in MongoDB to improve the performance of queries. An index can be created on a field in a collection to optimize the performance of queries that include that field.

18. What are the two types of indexes in MongoDB?

There are two types of indexes in MongoDB:

1. Primary Indexes: Every MongoDB document must have a primary index, which is used to uniquely identify each document.

2. Secondary Indexes: Secondary indexes can be used to store data that is frequently accessed but not necessarily required for every document.

19. What is the default index type in MongoDB?

The default index type in MongoDB is the B-tree index.

20. What happens if you try to create an index on a collection that doesn’t exist?

An error will be returned.