SQL Interview Questions and Answers

Hello everyone, today we are going to learn about SQL Interview Questions. As there are so many jobs available if you know SQL Language. SQL is a database language and which is used for programming with so many technologies such as Big Data. Big Data is an emerging technology that is used by most of the companies and organisations. So to get a job in Big Data field one of the ways is to learn SQL. So here I am going list down 15 SQL interview questions. All those who are going to appear for the interviews and their main stream they learnt is SQL then all of them can go through these SQL interview questions.

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SQL Interview Questions and Answers

Here are some of the basic and important SQL questions and answers that all of the aspirants who have learnt SQL language and want to enter in this field have to go through the interview. So, to qualify the interview round you need to have proper knowledge of the database language and its basics also. So below are the SQL interview questions and answers.

SQL Questions and Answers

  1. What is DBMS?

DBMS stands for Database Management System. It is a program that controls the creation, maintenance and use of the database. DBMS can be termed as the File Manager that manages all the data in the database rather than saving the data in file systems.

2. What is RDBMS?

RDBMS stands for the Relational Database Management System. RDBMS basically stores all the data it gets into the collection of the tables that is related by the common fields between the columns of a table. RDBMS also provides the relational operators to manipulate data stored in tables. An example of RDBMS is SQL Server.

3. What is SQL?

It stands for the Structured Query Language and this is basically used to communicate with the database. The language is used to perform some of the tasks such as retrieval, updation, insertion and eletion of the data sets from a database.

4. What is a database?

The database is an organised form of the data to have the easy access to data, storage, retrieval and managing the data. This is also referred as the structured type of data which can be accessed in many different ways.

For Example: School Management Database

5. What are tables and fields?

A table can be said as the data that is organised in a form of model with rows and columns. And further columns can be categorised as the vertical and rows can be categorised as the horizontal. A table can have any number of the rows that is called as a record but it can have specified the number of columns that is called as a field.

6. What is the Primary key?

It is a combination of the fields that uniquely specifies a row. The primary key is the special type of key that has implicit NOT NULL constraint. This actually means that primary key values cannot be NULL.

7. What is Unique Key?

Unique Key constraint identifies each record in a database. With this, it provides uniqueness for the column or set of columns.

8. What is Foreign Key?

A Foreign key is the one table that can be related to the primary key of the other table. This relationship needs to be created between the two tables by referencing the foreign key with the primary key of some other table.

9. What is Normalization?

Normalisation basically is the process of reducing the redundancy and also the dependency by organising the fields and tables of the database. The main purpose of the normalisation is to add, delete and to modify field which can be made into a single table.

10. What is Denormalization?

Denormalization is the technique which is used to access data from higher to the lower normal forms of the database. Denormalization is the process of introducing the redundancy into the table by incorporating the data from the related tables.

11. What is an Index?

An index is the method of performance tuning that allows faster retrieval of the records from the table. Index creates an entry for the each value and it becomes faster to retrieve the data,

12. What are the different types of indexes?

There are 3 types of the indexes that are listed below:

  • Unique Index: This type of index doesn’t allow field to have the duplicate values if the column is uniquely indexed. It can be applied automatically if the primary key is defined.
  • Clustered Index: Clustered index reorders physical order of table and search based on key values. Also, each table can have only one clustered index.
  • Non-Clustered Index: This type of the index doesn’t change the physical order of table and it also maintains the logical order of the data. Each table can have the 999 non-clustered indexes.

13. What is Cursor?

The cursor is the control that enables the traversal over rows or records in the table. It can be seen as the pointer to one row in the set of rows. The cursor is useful for the traversing like retrieval, addition and also the removal of database records.

14. What is a relationship and what are they?

Database Relationship can be defined as the connection between tables in the database. The different data basing relationships are:

  • One to One Relationship
  • One to Many Relationship
  • Many to One Relationship
  • Self Referencing Relationship

15. What is the difference between DELETE and TRUNCATE commands?

The command Delete is used to remove/ delete the rows from table and rollback and commit can also be done after delete command. Truncate is also used to remove/ delete all the rows from the table but the rollback cannot be performed after Truncate action.

So these were the top 15 basic as well as important question of SQL and this is not the end there are much more. So all those who are going to appear for SQL interviews should go through these SQL interview questions. Also if you want to learn about important Big data interview questions and answers or Hadoop interview questions and answers then you can check it from here. For any query, you can leave a comment below.


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