Introduction to Relational Database and SQL | What is SQL

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In this article, we will explore SQL in-depth, discussing its history, features, syntax, and practical applications. We will also look at some of the key concepts and best practices that are essential for using SQL effectively.

Table of Contents

As we know, SQL is a query programming language. So, first, we need to understand what is a query language, so we can better understand query language.

Introduction to Query Language

A query language is a computer programming language designed to retrieve and manipulate data from a database. It provides a way for users to interact with databases by specifying queries that request specific information from the database.

Query languages are used in a variety of contexts, including relational databases, graph databases, and document-oriented databases. Some popular query languages include SQL (Structured Query Language) for relational databases, Cypher for graph databases, and MongoDB Query Language for document-oriented databases.

Query languages typically use a syntax that is specific to the database management system being used. They allow users to specify which data they want to retrieve or modify, as well as any conditions or criteria that should be used to filter the data. By using query languages, users can access and manipulate data in a more efficient and precise manner than through manual searching or sorting.

Introduction to SQL

Structured Query Language (SQL) is a programming language designed to manage data stored in relational databases.

It is used to create, modify, and retrieve data from databases. SQL is widely used in the technology industry, and its importance cannot be overstated.

It is the backbone of many software applications and systems, and it is essential for anyone who wants to work with data.


SQL was first developed by IBM in the 1970s as a way to manipulate data stored in their System R database management system. However, it wasn’t until the 1980s that SQL began to gain widespread adoption as a standard language for relational databases.

In 1986, the American National Standards Institute (ANSI) released the first official SQL standard, known as SQL-86. This standard established the syntax and semantics of SQL and provided a common language for working with relational databases. Since then, several revisions of the SQL standard have been released, including SQL-89, SQL-92, SQL:1999, SQL:2003, SQL:2008, and SQL:2016.

Today, SQL is widely used in the technology industry and is supported by many database management systems, including Oracle, Microsoft SQL Server, MySQL, PostgreSQL, and SQLite.


SQL has several features that make it a powerful tool for working with data. Some of the key features of SQL include:

  1. Relational database management: SQL is designed to work with relational databases, which are used to store data in tables that are related to each other. This makes it easy to organize and manage large amounts of data.
  2. Data manipulation: SQL allows you to manipulate data stored in a database, including inserting, updating, deleting, and retrieving data.
  3. Data definition: SQL provides commands for creating and modifying database objects, such as tables, views, and indexes.
  4. Data control: SQL allows you to control access to data in a database, including setting permissions and managing user accounts.
  5. Transaction control: SQL supports transactions, which allow you to group multiple database operations into a single unit of work. This helps to ensure that the database remains consistent and accurate.


There are a few potential disadvantages of using SQL:

  1. Steep Learning Curve: SQL can be difficult to learn for beginners, especially those who don’t have a strong background in computer science or programming.
  2. Scalability: SQL databases can become slow and difficult to scale as data grows in size or complexity. As a result, it may be necessary to migrate to a more complex database management system.
  3. Limited Functionality: While SQL is great for managing and querying relational databases, it may not be suitable for other types of data, such as unstructured or hierarchical data.
  4. Security Risks: If an SQL database is not properly secured, it can be vulnerable to attacks such as SQL injection, resulting in data breaches or other security issues.
  5. Maintenance: SQL databases require regular maintenance, including updates, backups, and optimization, which can be time-consuming and costly.

SQL Process

The process of executing an SQL query involves several steps:

  1. Query Planning: The first step in the SQL process is query planning. In this step, the query is analyzed to determine the most efficient way to execute it. This includes identifying which tables must be accessed, which indexes should be used, and how the data should be sorted and grouped.
  2. Query Optimization: Once the query plan is created, the optimizer evaluates different execution plans to determine the most efficient one. This involves selecting the most efficient algorithms and techniques to access and manipulate the data.
  3. Query Execution: After the query is planned and optimized, it is executed. The database engine reads the data from the tables and applies any necessary filtering, grouping, and sorting operations. The results are then returned to the user or application that initiated the query.
  4. Result Fetching: The final step in the SQL process is fetching the results. The results of the query are returned to the user or application in the format specified in the query, such as a table or a list of values.

Throughout the SQL process, the database engine may use indexes, caches, and other optimization techniques to speed up the execution of the query. In addition, the database may use locking and concurrency control techniques to ensure that multiple users or applications can access the data simultaneously without conflicts or inconsistencies.

Rules for writing SQL Query

When writing an SQL query, it is important to follow certain rules to ensure that the query is structured correctly and returns the desired results. Here are some general rules to follow:

  1. Use clear and concise syntax: SQL syntax is a specific set of rules for writing SQL queries. Be sure to use the correct syntax to avoid errors and ensure that your query is easy to read and understand.
  2. Use appropriate keywords: Use the appropriate keywords such as SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY to indicate the different parts of the query.
  3. Use proper capitalization: Use consistent capitalization for SQL keywords and identifiers. Some prefer to use all uppercase, some prefer lowercase, and some prefer a combination of both. Whichever you choose, be sure to be consistent throughout your query.
  4. Use proper indentation: Use proper indentation to make your query easy to read and understand. Indent the SELECT, FROM, WHERE, GROUP BY, HAVING, and ORDER BY clauses.
  5. Use aliases: Use aliases for tables and columns to make your query easier to read and understand. For example, instead of writing “SELECT employee_name FROM employees,” you could write “SELECT e.employee_name FROM employees e.”
  6. Use comments: Use comments to explain your query and make it easier for others to understand. Comments are also useful for debugging and troubleshooting.
  7. Avoid using reserved keywords as identifiers: Avoid using reserved keywords as column or table names. Reserved keywords have special meanings in SQL, such as SELECT, FROM, WHERE, etc.
  8. Use single quotes for string values: Use single quotes to enclose string values in SQL. For example, ‘John Smith’ instead of “John Smith” or John Smith.
  9. Test your query: Always test your query to make sure it returns the desired results. Use sample data or a small subset of the data to test your query before running it on the entire dataset.

Following these rules will help you write SQL queries that are accurate, efficient, and easy to understand.


SQL is an essential tool for working with relational databases. It provides a powerful and flexible way to manage data stored in databases and is widely used in the technology industry. By following best practices and understanding the SQL process, you can use SQL effectively to solve problems and manage data in your organization.

Requirement for learning SQL

If you are frustrated with the installation of SQL software so don’t worry there are many online compilers available in which we can save our data and easily manipulate that data.

So, we are practicing SQL on this website.

For Practice Click Here


What is SQL?

Structured Query Language (SQL) is a programming language that is designed to manage data stored in relational databases.
It is used to create, modify, and retrieve data from databases. SQL is widely used in the technology industry, and its importance cannot be overstated.

What are the advantages of SQL?

1) Relational database management
2) Data manipulation
3) Data definition
4) Data control
5) Transaction control

What are the disadvantages of SQL?

1) Steep Learning Curve
2) Scalability
3) Limited Functionality
4) Security Risks
5) Result Fetching

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