SQL Interview Questions

Technical interviews for jobs tend to get a bit tricky especially when you take into consideration the various stages, namely Telephonic Interviews, technical and lastly personal Interviews. Further, they test not only concept-based knowledge but also skills of creative thinking, problem-solving, etc. Before appearing for an interview for any job role, it becomes essential to explore the field, in its present context as well as any recent modifications or changes it has witnessed. Through this blog, we will provide you with some of the most common SQL interview questions you can expect to encounter and how you can prepare for them with an impressive answer.

List of SQL Questions & Answers

Let’s begin with some of the basic questions that the interviewer might ask you related to varied aspects of database systems.

What is a Database?

A database is a collection of data in an organised manner generally accessible through a computer. It is used to make actions like storage, retrieval, editing, management and deletion of data trouble-free and on fingertips.

What is Database Management System [DBMS]?

A DBMS is the interface through which the user interacts with the database and performs his actions of creation, manipulation and other data operations. 

Mention the types of DBMS.

The most common types of DBMS are as follows:

• Relational DBMS
• Hierarchical DBMS
• Object-Oriented DBMS
• Network DBMS

What is RDBMS?

Standing for Relational Database Management System [RDBMS], it is a category of DBMS based on the relational model of data. It forms the basis for all prevalent database systems, namely, SQL, Oracle, Microsoft Access, IBM DB2, etc.

State some of the primary applications of database systems in daily life.

Database systems are being used in a variety of organisations including hospitals, retail stores, banks, transport and logistic companies, media outlets, etc. In particular, it supports transactions, information retrieval, inventory management, ticket bookings, security maintenance and so forth.

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What is SQL?

Structured Query Language [SQL] is the computer language used in relational database management systems in order to relay commands of addition, manipulation and deletion of data in the database. 

Say a few words on the history of SQL.

This is one of the frequently asked SQL interview questions in which you need to talk about how SQL came into being. It was designed and developed by Raymond Boyce and Donald Chamberlain in the 1970s both researchers at IBM. It was earlier known as SEQUEL. This came after E.F. Todd developed the relational model of data in 1970.

Other than SQL interview questions, if you are sitting for a technical interview for admission into advanced computer courses, check out our blog on Data Structure Interview Questions.

Talk about the key point of difference between SQL and MySQL?

While SQL is a standard language, MySQL is an RDBMS. 

What are tables, fields and records in a database?

In a database, data is stored in the form of tables. Herein, the columns are known as tables and rows are called records.

What is a constraint? Identify its levels.

Constraints are specific filters used to identify or modify data. This includes keys such as PRIMARY, UNIQUE, FOREIGN and so forth.

What is a primary key, foreign key and unique key?

PRIMARY Key: It is simply defined as a column or series of columns that are used in a table to locate and identify each and every row. Its values can’t be null.
UNIQUE Key: Specifically picks out a row in a table. Values returning null are allowed.

Advantages and Disadvantages of Stored Procedure?

Stored procedure can be used as a modular programming – means you can create once, store and call for several times whenever required. This supports faster execution instead of executing multiple queries. The disadvantage is that this reduces network traffic and provides better security to the data.

SQL Interview Questions for Freshers

While the above ones can be said to be popular in interviews as well as in aptitude tests for interviews, here are a few more SQL interview questions that you must keep the answers ready for.

• Mention the subsets in SQL.
• Define Data Definition Language [DDL]?
• Elaborate Data Manipulation Language [DML]?
• What is Data Control Language [DCL]?
• What are the SQL set operators?
• What are SQL joins? Mention its different types.
• What is normalisation and denormalisation?
• What are the entities?
• What are the relationships?
• What is an index? Mention its different types.
• Talk about the major points of distinction between clustered and non-clustered index in SQL.
• What is a trigger?
• What do you understand by ACID property in a database?
• What are the SQL operators?

Commands-Related Questions

Specific command-based tasks also form part of the SQL interview questions. Glance over the following to have a better idea.

• Write the command to count the records in the table?
• Talk about the key differences between DELETE and TRUNCATE commands in SQL?
• Do you find any similarity or difference between DROP and TRUNCATE commands?
• Are ‘BETWEEN’ and ‘IN’ commands different?
• What is ‘MERGE’?
• Mention two examples each of ‘BETWEEN’ and ‘IN’ commands.
• What is CLAUSE?
• What are the case manipulation functions, like LOWER, UPPER and INITCAP?
• What does the ALIAS command do?
• Jot down the command to fetch all alternate records.
• What is the role of the DISTINCT command?
• Write an example each making use of STUFF and REPLACE functions.
• How can you display the date in SQL?
• Explain AGGREGATE and SCALAR functions.

SQL Interview Questions for 5-year Experience

• What is the Difference between COALESCE() & ISNULL()?
• How do you generate file output from SQL?
• What is a correlated subquery?
• What is the OSQL utility?
• What is the difference between UNION and UNIONALL?
• Why do we use the OPEN XML clause?
• Explain UNION, MINUS, UNION ALL, INTERSECT?
• Write a Query to display the third max salary of an employee?
• Write a Query to display the number of employees based on the city?
• Write a Query to display the total salary of employees based on region?
• Can we disable a trigger? if yes HOW?
• Why do you need indexing? where is Stored and what do you mean by schema object? For what purpose we are using view?

Tricky SQL Interview Questions

• How to get the DDL of the table in Oracle?
• How to find the count of duplicate rows?
• How to display 1 to 100 Numbers with query?
• How to convert seconds into time format?
• How to calculate the number of rows in the table without using the count function?
• Display 4 to 7 records from the Employee table.
• What is query to fetch the last record of the table?
• How to get the number of Weekends of the current month?
• How to display Date in the DD-MON-YYYY table?
• What do you mean by data integrity?

FAQs

While these technical SQL interview questions can be exacting, being prepared in advance and having programming experience pays off. Seeking expert guidance for your job interview can be the right step in nailing it with a great impression. The mentors at Leverage Edu can lend you a helping hand in accentuating your resume by evaluating your profile as well as equipping you with quality job-related advice so that you ace your interview and fulfil your career aspirations.