How to Hire a Database Developer

Without databases, it is almost impossible to imagine modern information technologies. They are everywhere! Accordingly, more and more companies need high-quality database development. If you are reading this article, then you may be among them. But how do you hire a highly qualified database developer? What are the requirements for this role? What should you ask during the interview? Uncover the answers to these and other questions below.

What are databases for

Databases are used in all modern digital society sectors, from applications in mobile phones to sophisticated spacecraft flight control systems.

Server databases store a lot of valuable information, so they are required for many companies. Representatives of small and medium-sized businesses often turn to technical developers who can design a database, with the order to create it and ensure uninterrupted operation.

Growing organizations can use databases to move from the usual storage of data and basic transactions to the analysis of large amounts of data from multiple systems. They can use the data they collect for more profitable work, effective decision making, flexibility, and scalability.

What are the programming languages, platforms, and services involved

A database management system is used to create and work with information. It supports database languages ​​and is responsible for backing up and restoring information after crashes. The control system allows you to process user requests and display the necessary information instantly.

MySQL is one of the most well-known data managing systems and is used by companies like Facebook, Twitter, and Wikipedia. MySQL is convenient, fast, and flexible. It supports various types of tables and the number is continually increasing. That is one reason why MySQL is used in many projects.

The second most popular database management system is Oracle. It is stable, fast, and reliable. The system is characterized by high security and great data protection, so it’s no surprise that it's often used in the banking sector. Oracle is also distributed in retail, insurance, and telecommunications companies. This system occupies about 30% of the market.

The other databases, like PostgreSQL, SQL Server, MongoDB, SQLite, Redis, Elasticsearch, and Google BigQuery, are also quite popular.

Technical skills for database developers

The database developer performs two functions. The first one is the implementation of the functionality that is responsible for working with the database. To perform this task, the programmer must have the tools of a particular programming language that allows them to organize such interaction. For example, if the dev uses C#, he or she needs to be familiar with technologies such as ADO.NET and/or Entity Framework, as well as LINQ for SQL, LINQ for Entities. Also, this specialist must understand the basics of SQL.

The second function is database administration. This task includes database design, configuration, management, efficient use, optimization, security, data migration, and more. Such a specialist doesn't need to know the programming language of applications. At the same time, they must have a deeper knowledge of SQL, database management system, and understand the specifics of the architecture and operation of the database.

Basic database developer skills:

• - Design, configuration, administration and optimization of the database

• - Understanding the specifics of the architecture and functioning of the database

• - Knowledge of security issues related to access to the database

• - Experience with database query languages (SQL, etc.)

• - Knowledge of the universal markup language XML will be an advantage

• - Understanding of the UML modeling language

• - Knowledge of DBMS types

• - Experience working with a version control system like git

• - Knowledge of an applied programming language like C#

• - Experience with technologies that interoperate the application with the database (e.g., ADO.NET, Entity Framework, LINQ)

Database developers can be classified into three levels depending on work experience and skill set.

How much does it cost to hire a database developer 

The U.S. Bureau of Labor Statistics forecasts an 11% increase in database-related jobs by 2024, which is above average for all professions. Growth in this area will depend on the expanding needs of companies in different industries. Even greater job growth is projected in the direction of databases related to the development of cloud services at17%.

The level of an average wage is also growing year over year. According to the U.S. Department of Labor, the average annual income of database administrators at the beginning of 2019 was $81,710.

Sources:  Ziprecruiter.com,  Payscale.com

Database developer job description

We now know who the database developer is, their responsibilities, and what budget we should allocate for their work. Now let's find out how we can choose a perfect database developer for our project among other candidates.

Since the database is an essential part of your service, we must approach the process responsibly. Write a brief description of your company and let potential employees know what they will be dealing with. For the below example, assume you are looking for a database developer to work on a project in the FinTech field. Let's understand what skills and knowledge such a specialist must have.

Job description: Middle database developer

Responsibilities:

• - MySQL Database management

• - Database development PL / SQL, Oracle

• - Technical documentation writing

• - Optimization of packages, procedures, functions

• - Help stakeholders better understand their business priorities by providing accurate, data-based reports

Skills and qualifications:

• - Experience in creating a database architecture from scratch

• - Proficiency in developing ETLs using APIs

• - Python development background

• - Deep knowledge of ANSI SQL and PL/SQL

• - Background of optimizing complex queries on large amounts of data

• - Experience in developing database models, deep knowledge of database theory

• - Deep knowledge of XML

Personal qualities:

• - Engineering mindset

• - Perseverance

• - Responsibility

• - System approach to problem-solving

• - Ability to work in a team

• - Proactive mindset

Database developer interview questions to ask

Finally, we have reached the most important stage of hiring a developer - the job interview. Yes, sometimes it’s hard to pick the right one, but we hope the following questions will help you to resolve this matter.

Question 1. What database models do you know?

Answer: There are three types of database models: a relational model, a key-value model, and a hierarchical data model. 

The relational model has several advantages: it takes up little space, has a clear structure and mechanisms, uses a convenient SQL query language, and support for the multi-user approach. The disadvantage is its comparatively low speed.

The "key-value" model assumes that there is a key (usually a set of bytes) that is directly related to the only one value (usually another set of bytes). The advantages are that it works quickly due to the compression of data and has a clear structure. However, the inability to verify the data for consistency and much more complex logic of implementation seems to be significant shortcomings in many cases.

The hierarchical model has become popular recently. The main advantage of such a structure is in ergonomics: data is stored and retrieved from the database exactly as stored in application objects. The weaknesses of this model are the difficult navigation system and the complexity of information organization.

Question 2. What do you know about relational tables?

Answer: Relational tables have the following properties: 

• - each row of the table contains a description of one data element 

• - all columns of the table have the same type and length

The names of the columns must be unique as well as rows and records about one element. The order of the rows and columns in the table does not matter and therefore, can be arbitrary.

Question 3. Under what conditions can the size of the SQL database file be reduced?

Answer: The amount of data may change if table numbers and record numbers are excluded. You should run a SQL query like: 'select count (1) from "TABLES_NAME";' ==> to check the number of records in one table. 

Another option is to run an optimization, reduction, or reorganization in the database, as this reduces the size of the database file.

Question 4. What function does the GRANT command perform in MySQL?

Answer: The GRANT command allows system administrators to create MySQL users and grant or revoke rights to users. GRANT has been included in MySQL since version 3.22.11 and above. In earlier versions of MySQL, the GRANT statement does nothing.

Question 5. What is the best way to remove duplicate records in an Oracle spreadsheet?

Answer: The best way is to use correlated queries and ROW_ID if table X has a huge number of records, and you want to delete a few from it.

Question 6. Which database is suitable for high-speed JSON operations?

Answer: The most suitable database for JSON is Mongo. As the NoSQL database management system, it has great speed performance. Moreover, MongoDB uses the lightweight BSON, an extension of JSON, for higher productivity.

Question 7. What do you know about partitioning database memory structures in Oracle?

Answer: Oracle uses "schemas" for logical separation. Table space is used for physical partitioning. At the same time, logical and physical partitions operate independently. You can store all schemas in one set of files, or you can divide them into several, for example, to extract archive tables on slower media or separate indexes from the data. In this case, you normally don't need to create a second copy on the same machine.

Question 8. Imagine you have been assigned a task to transfer a database from one server to another using a graphical interface.  How would you approach it?

Answer: You can solve the problem by making Backup-Restore.

Select the period without activity associated with the database (night), make a backup on the server you want to leave. 

How to backup: right-click on the database name in SSMS -> Tasks -> Back Up, in the window that appears, select where we want to backup and how. Expand the backup on the target server: right-click on the Databases directory name in SSMS -> Select a backup file to restore.

Question 9. Does the order of JSON elements matter?

Answer: There is no such thing as “element order” in relational databases. The order of loading into the database, the order of physical storage on the disk, and the order of issue are not concepts related to each other. No relational database guarantees this order. Accordingly, if this order is important, you must take care of it yourself. For example, add the data_number field to the data table, which will contain the serial number, and fill it yourself. When selecting, set the desired sorting structure.

Question 10. What is the difference between SGA and PGA in Oracle?

Answer: The main difference between SGA and PGA is that PGA is used only for the requirements of a particular process, while SGA is used for the entire instance.

Summing Up

Small, medium, and large companies are increasingly requiring the development of databases, as information must not only be stored but also processed and protected. Therefore, the demand for database developers is quite high. Hiring a specialist in this field may seem difficult, but a good database developer is a professional who will make your service more robust and reliable.