Frequently Asked SQL Interview Questions with Answers

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Appearing for an interview can be a nerve-racking experience, especially if you feel under-prepared about the questions that the interviewer is likely to ask you. This is especially true if you are appearing for an interview for a vast subject such as database management systems and programming. One of the areas where a lot of people face challenges is SQL. Structured Query Language (SQL) is a programming language, which is domain-specific and used for managing data in the Database Management Systems (DBMS). SQL programming skills are one of the much sought-after skills as DBMS is used in all software applications. It is good to go through some frequently asked SQL interview questions before the interview to have an idea about the topic.

If you have been preparing for an SQL interview, here are some frequently asked SQL Interview Questions that may help you get your grips on the subject and revise before the fateful interview.

Describe what is SQL?

Structured Query Language or SQL is used for communicating with the database. This is a standard language used for performing various tasks such as retrieval, updating, inserting, and deleting data from a database. It is one of the most common and frequently asked SQL query interview questions that you can expect from most interviewers.

What is a Database?

The database is an organized form of data so that data can be easily accessed, stored, and managed. You can also call it a structured form of data that you can access in several ways. It has various business applications that make it valuable.

What is Database Management Systems?

Database Management Systems, commonly called DBMS, are programs that help in creating, maintaining, and using a database. You can also call it a File Manager with the help of which data in the database can be managed. This is among frequently asked SQL interview questions for freshers.

What is Relational Database Management System?

Relational Database Management System, also commonly called RDBMS, is a database type where the data is shared in tables and can be identified and accessed in relation to another data set or database. In an RDBMS, the columns act as the common field and can be accessed through SQL language.

What are tables and fields?

A table can be explained as a set of data that has been organized with columns and rows. Columns are vertical while rows are horizontal. In a table, the specified number of columns is called fields. The same table can have any number of rows, called a record.

What is a primary key?

When a set of fields specify a row, the combination is known as a primary key. The value of the primary key cannot be NULL, as it has a constraint of NOT NULL.

What is the difference between a Primary and a Foreign key?

A Foreign key is different from a Primary key since a Foreign key is a table that is related to the Primary key of a different table. To establish a relationship between two tables, the Foreign Key of one table is referenced to the Primary Key of another table. This is another frequently asked SQL server interview questions that is often asked during interviews by prospective employers.

What does a Unique Key mean in SQL?

Each record of the database is uniquely identified by the Unique Key constraint. A column or column set gets unique with a Unique Key. The unique constraint is automatically defined on the Primary key; however, not on the Unique Key. Each table can have only one Primary key constraint compared to the unique constraint which can be many per table.

What is Join and what are the types of Join?

Join is used for retrieving data based on the relationship between tables according to the keys. Based on the relationship between the fields of the table, Join acts as a keyword while querying data from more tables. There are different types of joins based on the relationships between tables. Examples of joins are Inner Join, Right Join, Left Join, and Full Join.

How can you create a table in SQL?

To create a table in SQL, you can use the CREATE TABLE command as shown below.

CREATE TABLE <table_name> 

This is followed by putting the columns along with data types.

How can you delete a table in SQL?

Often asked in quick succession to the previous question, the interviewer is evaluating your response. Your answers should be along the lines of the following.

For deleting a table in SQL, DROP and TRUNCATE are the two commands that are used. DROP TABLE deletes the entire table from the database along with the data. On the other hand, you can use the TRUNCATE TABLE command to delete the data while preserving the table.

What is Normalize in SQL?

Normalize removes all the redundant data from a table by creating simple and small tables by decomposing a complex and large table.

Although SQL is a vast subject that takes time to understand, learn and master; these frequently asked SQL interview questions will surely help you prepare for any upcoming interview. Do check out the Great Learning Academy for a more detailed tutorial of the applications and fundamentals of SQL.

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