SQL Interview Questions and Answers 2023

LISTEN TO THE SQL FAQs LIKE AN AUDIOBOOK

In this data-centric world, there has been an escalating demand for SQL professionals with strong analytical thinking skills. Considering the ever-growing community of SQL, a career in SQL seems to be a promising path that offers lucrative salaries. So, if you’re thinking of starting a SQL career, you must master all SQL concepts.

We have compiled an extensive list of SQL Interview Questions to help you kickstart a SQL career. These SQL interview questions and answers will advance your SQL knowledge and help you succeed in your next SQL interview.

Once you prepare the questions mentioned in our list, you will be all set to get into various job roles such as Data Scientist, BI Reporting Engineer, Database Administrator, Quality Assurance Tester, SQL Developer, Business Analyst, BI Solution Architect, etc.

What are the reasons to learn SQL?

Learning pl/sql interview questions can be beneficial in many ways, such as:

  • Numerous job opportunities: SQL is a fundamental skill required for many job roles in the IT industry, such as data analyst, database administrator, business analyst, data scientist, and software developer. Thus, developing your knowledge of SQL can increase your job opportunities.
  • Sought-after skill: Many businesses today rely on professionals who can make data-driven decisions to help them grow. Practicing SQL concepts can make you competent in extracting insights from data, analyzing it, and making informed decisions based on the data. Learning this in-demand skill and preparing basic SQL interview questions will only make you a competitive candidate.
  • Effective data management: SQL is a language used for managing and manipulating relational databases. By developing SQL skills, you can efficiently manage and extract valuable insights from data stored in databases, which is essential for effective decision-making in many industries.
  • Automating repetitive tasks: SQL can be used to automate repetitive tasks, such as data entry, updating data, and generating reports. You can automate these tasks and save time by developing SQL skills.
  • Improved communication: SQL is a standardized language used in the tech industry. SQL competency allows you to communicate more effectively with other professionals in the industry and better understand their work.

Overall, developing SQL skills is essential for anyone interested in a technology or data analysis career. It enables you to efficiently manage data, make informed decisions, automate tasks, and communicate effectively with other professionals in the industry.

 Top Career Prospects in SQL

Once you master all the commonly asked SQL Interview Questions, you can apply for various high-paying jobs, such as:

  • Data Scientist ($130556 per year)
  • BI Developer ($93256 per year)
  • Database Architect ($1,20,813 per year)
  • Database Administrator ($92,344 per year)
  • SQL Server Developer ($81,551 per year)
  • Quality Assurance Tester ($63104 per year)
  • Business Analyst ($83382 per year)
  • AWS Expert ($159,033 per year)
  • .Net Developer ($114831 per year)
  • BI Solution Architect ($103731 per year)
  • Big Data Engineer ($133,279 per year)

What can you expect in an SQL Interview?

In an SQL interview, you can expect basic and advanced SQL Interview Questions related to a wide range of topics related to:

  • Basic SQL syntax: The hiring manager may ask you to write basic SQL statements to demonstrate your understanding of syntax and the ability to retrieve and manipulate data from a database.
  • Database design and normalization: SQL job seekers are expected to design a database schema, normalize data tables, and explain the benefits of normalization.
  • SQL functions and operators: The recruiter may ask questions about SQL functions such as aggregate functions, string functions, date/time functions, and operators like UNION, JOIN, and subqueries.
  • Data analysis and reporting: You may be asked to write SQL queries to generate reports, analyze data, and answer business-related questions.
  • Security and access control: Expect questions regarding SQL security and access control, including topics like user authentication, authorization, and encryption.
  • Advanced SQL concepts: You may also be asked about advanced SQL concepts like stored procedures, triggers, and views.

In addition to technical interview questions, prepare behavioral questions that will evaluate your communication skills, problem-solving ability, and teamwork skills. It's important to come prepared with examples of how you have used SQL in real-world situations and demonstrate your ability to communicate technical concepts clearly and concisely.

How to ace an SQL Interview?

There are various steps you can take to get through an SQL interview and increase your chances of success:

  • Build a strong foundation: To succeed in an SQL interview, you need to have a strong understanding of the basics of SQL, including how to write and execute basic queries, how to work with tables and views, and how to use SQL functions and operators. Ensure you have a good grasp of these fundamentals by practicing basic SQL interview questions before you start applying for SQL-related jobs.
  • Highlight your experience: When applying for SQL-related jobs, ensure to highlight any relevant experience you have, such as previous work with databases or experience using SQL in a programming language.
  • Practice with sample databases: There are many sample databases available online that you can use to practice your SQL skills. Download one or more of these databases and practice writing queries and performing various SQL operations on them.
  • Emphasize your problem-solving skills: SQL is often used to solve complex problems and answer important questions. Showcase your problem-solving skills during the interview, and provide examples of how you have used SQL to solve previous challenging problems.
  • Stay up-to-date on the latest trends: The field of SQL is constantly evolving, so it's essential to stay up-to-date on the latest trends and best practices. Follow industry publications and blogs, and participate in online forums and communities to stay current.
  • Be confident and professional: Don’t let nervousness ruin your job interview. Show your interviewer that you are passionate about SQL and committed to excellence and that you’re eager to contribute to the success of the organization.

Apart from preparing frequently asked SQL Interview Questions and answers, follow the above steps that can help you secure an SQL job.

If you want to launch a successful SQL career, check out our compiled list of pl/sql interview questions.

Answer:

SQL stands for Structured Query Language. It is the standard language for RDBMS and is useful in handling organized data that has entities or variables with relations between them. SQL is used for communicating with databases.

Answer:

Database is nothing but an organized form of data for easy access, storing, retrieval and managing of data. This is also known as structured form of data which can be accessed in many ways.

Answer:

DBMS stands for Database Management System is the software that allows storing, modifying, and retrieving data from a database. And it is a group of programs that act as the interface between data and applications. DBMS supports receiving queries from applications and retrieving data from the database.

RDBMS stands for Relational Database Management System, Like DBMS, RDBMS is also the software that allows storing, modifying, and retrieving data from a database but a RELATIONAL database. In a relational database, the data in the tables have a relationship. Besides, RDBMS is useful when data in tables are being managed securely and consistently.

Answer:

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.

Answer:

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 the creation of the table or after creating using the ALTER TABLE command. The constraints are:

  • NOT NULL– Restricts NULL value from being inserted into a column.
  • CHECK– Verifies that all values in a field satisfy a condition.
  • DEFAULT– Automatically assigns a default value if no value has been specified for the field.
  • UNIQUE– Ensures unique values to be inserted into the field.
  • INDEX– Indexes a field providing faster retrieval of records.
  • PRIMARY KEY– Uniquely identifies each record in a table.
  • FOREIGN KEY– Ensures referential integrity for a record in another table.

Answer:

Data Integrity is the assurance of accuracy and consistency of data over its entire life-cycle and is a critical aspect of 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.

Answer:

The following are the four significant subsets of the SQL:

  • Data definition language (DDL): It defines the data structure that consists of commands like CREATE, ALTER, DROP, etc.
  • Data manipulation language (DML): It is used to manipulate existing data in the database. The commands in this category are SELECT, UPDATE, INSERT, etc.
  • Data control language (DCL): It controls access to the data stored in the database. The commands in this category include GRANT and REVOKE.
  • Transaction Control Language (TCL): It is used to deal with the transaction operations in the database. The commands in this category are COMMIT, ROLLBACK, SET TRANSACTION, SAVEPOINT, etc.

Answer:

Normalization is used to minimize redundancy and dependency by organizing fields and table of a database.

There are some rules of database normalization, which is commonly known as Normal Form, and they are:

  • First normal form(1NF)
  • Second normal form(2NF)
  • Third normal form(3NF)
  • Boyce-Codd normal form(BCNF)

Using these steps, the redundancy, anomalies, inconsistency of the data in the database can be removed.

Answer:

An Inconsistent dependency refers to the difficulty of getting relevant data due to a missing or broken path to the data. It leads users to search the data in the wrong table, resulting in an error as an output.

Answer:

If a table is dropped, all things associated with that table are dropped as well. This includes the relationships defined on the table with other tables, access privileges, and grants that the table has, as well as the integrity checks and constraints. To create and use the table again in its original form, all the elements associated with the table need to be redefined.

However, if a table is truncated, there are no such problems as mentioned above. The table retains its original structure.

Answer:

The trigger can be defined as an automatic process that happens when an event occurs in the database server. It helps to maintain the integrity of the table. The trigger is activated when the commands, such as insert, update, and delete, are given.

The syntax used to generate the trigger function is:

CREATE TRIGGER trigger_name

Answer:

Relationships are developed by interlinking the column of one table with the column of another table. There are three different types of relationships, which are as follows:

  • One-to-one relationship
  • Many-to-one relationship
  • Many-to-many relationship

Answer:

Two authentication modes are available in SQL Server. They are:

  • Windows Authentication Mode: It allows authentication for Windows but not for SQL Server.
  • Mixed Mode: It allows both types of authentication—Windows and SQL Server.

Answer:

A function is an SQL Server database object. It is basically a set of SQL statements that allow input parameters, perform processing, and return results only. A function can only return a single value or table; the ability to insert, update, and delete records in database tables is not available.

Answer:

The primary key and unique key both are essential constraints of the SQL. The main difference among them is that the primary key identifies each record in the table. In contrast, the unique key prevents duplicate entries in a column except for a NULL value.

Answer:

There are four different types of JOINs in SQL, which are as follows:

  • Inner Join– Inner join return rows when there is at least one match of rows between the tables.
  • Right Join– Right join return rows which are common between the tables and all rows of Right hand side table. Simply, it returns all the rows from the right hand side table even though there are no matches in the left hand side table.
  • Left Join– Left join return rows which are common between the tables and all rows of Left hand side table. Simply, it returns all the rows from Left hand side table even though there are no matches in the Right hand side table.
  • Full Join– Full join return rows when there are matching rows in any one of the tables. This means, it returns all the rows from the left hand side table and all the rows from the right hand side table.

Answer:

Stored Procedure is a function consists of many SQL statement to access the database system. Several SQL statements are consolidated into a stored procedure and execute them whenever and wherever required.

Answer:

Database Cardinality denotes the uniqueness of values in the tables. It supports optimizing query plans and hence improves query performance. There are three types of database cardinalities in SQL, as given below:

  • Higher Cardinality
  • Normal Cardinality
  • Lower Cardinality

Answer:

Following are the different types of cursors:

  • Forward Only: It is known as the firehose cursor that can make only a forward movement. The modification made by the current user and other users is visible while using this cursor. As it is the forward-moving cursor, it fetches rows of the result set from the start to end serially.
  • Static: This cursor can move forward and backward on the result set. Here, only the same result set is visible throughout the lifetime of the cursor. In other words, once the cursor is open, it doesn’t show any changes made in the database that is the source for the result set.
  • Keyset: This cursor is managed by a set of identifiers known as keys or keysets. Here, the keysets are built by the columns that derive the rows of a result set. When we use this cursor, we can’t view the records created by other users. Similarly, if any user deletes a record, we can’t access that record too.
  • Dynamic: Unlike static cursors, once the cursor is open, all the modifications performed in the database are reflected in the result set. The UPDATE, INSERT and DELETE operations made by other users can be viewed while scrolling the cursor.

Answer:

The schema represents the logical structures of data. Using schemas, the database objects can be grouped logically in a database. Schema is useful for segregating database objects based on different applications, controlling access permissions, and managing a database’s security aspects. Simply out, Schemas ensure database security and consistency.

Following are the advantages of Schema in SQL:

  • Schemas can be easily transferred.
  • You can transfer database objects between schemas.
  • It protects database objects and achieves effective access control.