SQL Developer Interview Questions

Responsibilities

 SQL developer responsibilities may include:

• Designing database tables to store application data
• Creating optimized queries
• Creating table indexes
• Building database systems
• Providing data modeling to help map out database structure
• Creating triggers for database automation

Skills

SQL is necessary to provide interactive web designs. In order to streamline databases to provide a pleasant user experience, skilled SQL developers will:

• Communicate effectively with other engineers on their team
• Possess an eye for detail to identify errors in code
• Utilize creative thinking to automate processes
• Work quickly to solve code issues as quickly as possible when a site is live
• Identify weak points within the database

Qualifications

Candidates for SQL developer positions are strongly advised to possess at least a bachelor’s degree in computer science due to the competitive nature of the job. Additionally, candidates may obtain certifications from third-party vendors such as the Microsoft Certified Technology Specialist credential.

If you’re getting ready to interview for a position as an SQL developer, you can prepare by researching the company as much as possible. Learn about the 9 things you should research before an interview.

Salary

Salaries for SQL developers range between $54K and $117K with the median being $92K. 

Factors impacting the salary you receive as an SQL developer include:

• Degrees  (associate's or an equivalent certificate, bachelor's, BS, master's, MS)
• Years of Experience
• Location
• Reporting Structure (seniority of the manager you report to, number of direct reports such as junior developers or technicians, etc.)
• Level of Performance - exceeding expectations

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SQL Developer Interview Questions

Question: Can you give me your definition of SQL and a database?

Explanation: This is a technical question that is usually asked early in the interview to confirm that you have experience in this field. It's also used as a conversation starter, and it provides the interviewer with a sample of your communication skills, the knowledge of which they will use during the rest of the interview.

Example: “SQL stands for structured query language. This is used to retrieve and send information in order to manage databases. A database is a collection of information stored in a structured format that enables the data to be manipulated, retrieved, and used for analysis or data-driven decision making.”

Question: What are the differences between a DBMS and RDBMS?

Explanation: An interviewer will ask this question to determine your depth of knowledge as an SQL Developer as well as your understanding of the different tools used in this profession. Since this is a technical question, your answer should be in the form of a definition with little or no embellishment.

Example: “DBMS stands for database management system which is software responsible for the creation, retrieval, updates, and management of a database. It serves as an interface between the database and application software. RDBMS is a relational database management system that stores data in the form of a collection of tables and the relationships defined between the common fields of the tables. This table structure is the main difference between these two tools.”

Question: Can you name the commands which are important for managing a database in SQL?

Explanation: This is yet another technical question. When preparing for each interview as an SQL developer, you can anticipate that the majority of the questions you will be asked will be technical questions. You can answer this question based on the commands you have used in the past if you have experience in SQL. Otherwise, state the most common commands used in this field, based on your training and education.

Example: “The commands used most often in my work as an SQL developer fall into the categories of data definition, transaction control, data query, data manipulation, and data control. Specific commands I use quite often are create, alter, drop, rename, truncate, and copy.”

Question: In your opinion, what are the key factors affecting the functionality of a database?

Explanation: Although this is a technical question, it is asking for an opinion and is therefore subjective. While there is no right answer to this type of question, it will provide the interviewer with an indication of both your knowledge of databases and your preferences.

Example: “One of the key factors of a database is its size and ability to store data. The larger the database, the more complex it becomes to manage. This is where SQL becomes helpful because it allows us to manage and manipulate large datasets. While SQL doesn’t eliminate the complexity of large databases, it will certainly help minimize its impact.”

Question: How is the join command used in SQL, and what are the variations of this command?

Explanation: The interviewer is continuing to ask technical questions to confirm your skills as an SQL developer. Again, these should be easy to answer based on your experience, education, and preparation for the interview. It’s a good idea to review common SQL commands in advance of an interview.

Example: “Join is a simple query used to retrieve columns and rows from a database. It is useful when you are required to manage a large number of tables simultaneously. Variations of the join command include right join, inner join, left join, outer join, and upper join.”

Question: What is the difference between an index and a view, and how are each used within SQL?

Explanation: This question digs a little deeper into your technical acumen and knowledge of the SQL language. The interviewer will ask more difficult technical questions as they become satisfied with your level of competency as an SQL developer.

Example: “Indexes are created on columns within the database and enable faster queries and quick retrieval of the data within the table.  Views, on the other hand, are subsets of the table whose purpose is logically storing the database. These can be thought of as virtual tables containing both rows and columns. Keep in mind that views don’t actually contain data that belongs to them but are merely representations of the table.”

Question: Following up on my last question, what are some of the benefits of views and an SQL application?

Explanation: Since the majority of questions will be technical ones, you should anticipate follow-up questions like this one. This provides the interviewer the opportunity to delve deeper into a topic. It also indicates that this particular technology or function is important to the company’s operations. You answer this question just like you answer the other technical questions.

Example: “The best feature of views is they do not consume much space so they can be used without impacting the overall performance of the SQL app. Additionally, they provide users a simple way to retrieve information without the complexity of creating an SQL query.”

Question: Can you describe the different types of SQL statements and how they are used?

Explanation: Another technical question that asks about a specific feature of SQL. Use a straightforward answer, providing the definitions and a brief statement of how the statements are used. If the interviewer needs more information, they will request it in a follow-up question.

Example: “There are five types of SQL statements. These include data query language or DQL which retrieves the data, data definition language or DDL which is used to define the structure that holds the data, data manipulation language or DML which is used to manipulate the data, data control language or DCL which is used to control the visibility of the data, and finally, TCL which stands for transaction control language which manages data transactions.”

Question: Two commands are used to delete data in SQL. These are delete and truncate. Can you tell me the difference between them?

Explanation: On the surface, this appears to be a trick question, but it isn’t. Experienced SQL developers should know the difference between these two commands that roughly do the same thing. Knowing the answer will demonstrate your in-depth skills as an SQL developer.

Example: “While both of these commands can delete data, they do it in different ways. Delete is a DML command used to delete all the records row by row. You can also use it to delete a specific record. The disadvantage of this command is that it runs slower than truncate. Truncate, on the other hand, is a DDL command used to delete all of the records at a single time. The disadvantage of truncate is that it cannot be used to delete a single record.”

Question: There are two types of tests used in most SQL operations. They are database testing and GUI testing. Can you describe the difference between them?

Explanation: This is more of an operational question in which the interviewer is seeking to assure themselves that you perform tests while managing a database. Knowing the difference between these two types of tests will indicate that you’ve run both of them in the past.

Example: “The main difference between them is that GUI testing is performed on the front end while database testing takes place on the backend. Additionally, GUI testing involves items visible to the users while database testing uncovers invisible or unseen errors. Finally, database testing is an SQL function, whereas GUI testing isn’t.”

Additional SQL Developer Interview Questions

• What is an execution plan?

• Explain each of the ACID properties.

• What is ASCI code for the line feed?

• What is the difference between truncate and delete?

• Can you remove duplicate records if needed?