Top 37 SQL Interview Questions And Answers 2023

SQL stands for Structured Query Language. It is a domain-specific language that is used to manage the data in Data Management Systems. Since there is a massive requirement for Data Management Systems in the market right now, the need for SQL programming skills has been increased significantly.
Given the requirement in the market, a lot of people have opted for SQL for their major. All they want is to get a job requiring SQL skills and they would certainly hope for a handsome salary too.
But getting a job in today’s time is no joke. You need to be qualified enough and then you need to make the employers believe that you are qualified enough and right for the job as well. This is done by taking an interview. No matter for which job you are applying for, all you need is to crack the interview first. Which might one of the most difficult part as well because you would be competing against many other candidates and some them would be just as qualified as you are. That’s where the problem starts. You need to compete against the other candidates and make the employers believe that you are better than others. This, too, depends on your SQL interview.
We are sure that you would be doing everything in your power to prepare for the interview and get the job. But this isn’t that easy, no? All you would be thinking is how would the interview go? Will you get the job? What kind of questions do they ask in an SQL interview?
Well, we are here for the last common worry of job candidates that is what kind of questions they ask in SQL interview.
In this article, we are going to provide you a list of SQL interview questions. These questions would help you to prepare for the interview better and you would already have some idea about the questions asked in SQL interviews.
What are you waiting for? Go ahead and take a look at the following list of SQL Interview Questions and be ready for the next interview.
SQL interview questions
[toc]

SQL Interview Questions

What is SQL?
Ans-
SQL stands for Structured Query Language. It is the standard language for relational database management systems. It is especially useful in handling organized data comprised of entities (variables) and relations between different entities of the data.
What is the difference between SQL and MySQL?
Ans-
SQL is a standard language for retrieving and manipulating structured databases. On the contrary, MySQL is a relational database management system, like SQL Server, Oracle or IBM DB2, that is used to manage SQL databases.
What are Tables and Fields?
Ans-
A table is an organized collection of data stored in the form of rows and columns. Columns can be categorized as vertical and rows as horizontal. The columns in a table are called fields while the rows can be referred to as records.
What are Constraints in SQL?
Ans-
Constraints are used to specify the rules concerning data in the table. It can be applied for single or multiple fields in an SQL table during creation of table or after creationg using the ALTER TABLE command.
What is Database?
Ans-
A database is an organized collection of data, stored and retrieved digitally from a remote or local computer system. Databases can be vast and complex, and such databases are developed using fixed design and modeling approaches.
What is DBMS?
Ans-
DBMS stands for Database Management System. DBMS is a system software responsible for the creation, retrieval, updation and management of the database. It ensures that our data is consistent, organized and is easily accessible by serving as an interface between the database and its end users or application softwares.
What is RDBMS? How is it different from DBMS?
Ans-
RDBMS stands for Relational Database Management System. The key difference here, compared to DBMS, is that RDBMS stores data in the form of a collection of tables and relations can be defined between the common fields of these tables. Most modern database management systems like MySQL, Microsoft SQL Server, Oracle, IBM DB2 and Amazon Redshift are based on RDBMS.
What is a Primary Key?
Ans-
The PRIMARY KEY constraint uniquely identifies each row in a table. It must contain UNIQUE values and has an implicit NOT NULL constraint.
A table in SQL is strictly restricted to have one and only one primary key, which is comprised of single or multiple fields (columns).
What is a UNIQUE constraint?
Ans-
A UNIQUE constraint ensures that all values in a column are different. This provides uniqueness for the column(s) and helps identify each row uniquely. Unlike primary key, there can be multiple unique constraints defined per table. The code syntax for UNIQUE is quite similar to that of PRIMARY KEY and can be used interchangeably.
What is a Foreign Key?
Ans-
A FOREIGN KEY comprises of single or collection of fields in a table that essentially refer to the PRIMARY KEY in another table. Foreign key constraint ensures referential integrity in the relation between two tables.
The table with the foreign key constraint is labelled as the child table, and the table containing the candidate key is labelled as the referenced or parent table.

Sql Interview Questions For developers

What is the difference between Clustered and Non-clustered index?
Ans-
As explained above, the differences can be broken down into three small factors –
Clustered index modifies the way records are stored in a database based on the indexed column. Non-clustered index creates a separate entity within the table which references the original table.
Clustered index is used for easy and  speedy retrieval of data from the database, whereas, fetching records from the non-clustered index is relatively slower.
In SQL, a table can have a single clustered index whereas it can have multiple non-clustered indexes.
What is Data Integrity?
Ans-
Data Integrity is the assurance of accuracy and consistency of data over its entire life-cycle, and is a critical aspect to the design, implementation and usage of any system which stores, processes, or retrieves data. It also defines integrity constraints to enforce business rules on the data when it is entered into an application or a database.
What is a Query?
Ans-
A query is a request for data or information from a database table or combination of tables. A database query can be either a select query or an action query.
What is recursive stored procedure?
Ans-
A stored procedure which calls by itself until it reaches some boundary condition. This recursive function or procedure helps programmers to use the same set of code any number of times.
What is Union, minus and Interact commands?
Ans-
UNION operator is used to combine the results of two tables, and it eliminates duplicate rows from the tables.
MINUS operator is used to return rows from the first query but not from the second query. Matching records of first and second query and other rows from the first query will be displayed as a result set.
INTERSECT operator is used to return rows returned by both the queries.
Advantages and Disadvantages of Stored Procedure?
Ans-
Stored procedure can be used as a modular programming – means create once, store and call for several times whenever required. This supports faster execution instead of executing multiple queries. This reduces network traffic and provides better security to the data.
Disadvantage is that it can be executed only in the Database and utilizes more memory in the database server.
What is Online Transaction Processing (OLTP)?
Ans-
Online Transaction Processing (OLTP) manages transaction based applications which can be used for data entry, data retrieval and data processing. OLTP makes data management simple and efficient. Unlike OLAP systems goal of OLTP systems is serving real-time transactions.
Example – Bank Transactions on a daily basis.
What is CLAUSE?
Ans-
SQL clause is defined to limit the result set by providing condition to the query. This usually filters some rows from the whole set of records.
Example – Query that has WHERE condition
Query that has HAVING condition.
What is recursive stored procedure?
Ans-
A stored procedure which calls by itself until it reaches some boundary condition. This recursive function or procedure helps programmers to use the same set of code any number of times.
What is the difference between Cluster and Non-Cluster Index?
Ans-
Clustered index is used for easy retrieval of data from the database by altering the way that the records are stored. Database sorts out rows by the column which is set to be clustered index.
A nonclustered index does not alter the way it was stored but creates a complete separate object within the table. It point back to the original table rows after searching.
What is Datawarehouse?
Ans-
Datawarehouse is a central repository of data from multiple sources of information. Those data are consolidated, transformed and made available for the mining and online processing. Warehouse data have a subset of data called Data Marts.
What is Self-Join?
Ans-
Self-join is set to be query used to compare to itself. This is used to compare values in a column with other values in the same column in the same table. ALIAS ES can be used for the same table comparison.
What is Cross-Join?
Ans-
Cross join defines as Cartesian product where number of rows in the first table multiplied by number of rows in the second table. If suppose, WHERE clause is used in cross join then the query will work like an INNER JOIN.
What is user defined functions?
Ans-
User defined functions are the functions written to use that logic whenever required. It is not necessary to write the same logic several times. Instead, function can be called or executed whenever needed.

Conclusion –

So these are some of the most commonly asked SQL interview questions that you can find. These questions have been handpicked by some experts and professionals who are willing to help young candidates to get the job of their dreams. Now that you are aware of a few common questions in SQL interview questions, all you need is to prepare the perfect answer for the questions.
We hope you found our article helpful and now that you know what kind of questions they generally ask, you can prepare for the upcoming interview as well. Best of luck with your SQL interview questions and we hope you crack the interview with flying colors.

Leave a Comment