Computer Study

What is SQL, History, Process, SQL Commands, Advantages, Disadvantage

What is SQL?

SQL (Structured Query Language) is a programming language used to manage and manipulate relational databases. It is the standard language for managing data stored in relational database management systems (RDBMS). SQL is used to create, modify, and delete databases, tables, and data. It also allows users to query and retrieve data from databases based on various criteria.

Why SQL?

SQL is widely used because it offers a standardized way to manage and manipulate data in relational databases. It is easy to learn and use, and has powerful querying capabilities that allow users to retrieve specific data from large and complex databases.

History of SQL

SQL was developed in the 1970s by IBM researchers as a way to manage data stored in relational databases. The first commercial implementation of SQL was released in 1979 by Oracle Corporation, and it quickly became the standard language for managing data in relational databases.

Process of SQL

The process of using SQL typically involves the following steps:

  1. Defining the database structure: This involves creating the database and its tables, and defining the relationships between the tables.
  2. Populating the database: This involves inserting data into the tables.
  3. Querying the database: This involves retrieving data from the database based on various criteria, such as selecting specific columns, filtering rows based on certain conditions, and joining tables.
  4. Modifying the database: This involves updating or deleting data in the database.

Structured Query Language (SQL) is a powerful programming language used for managing and manipulating relational databases.

It contains four main components in its process, which work together to ensure that SQL queries are executed efficiently and effectively.

These components are the Query Dispatcher, Optimization Engines, Classic Query Engine, and SQL Query Engine.

The Query Dispatcher is the first component in the SQL process. Its main role is to receive the SQL query from the user and pass it on to the appropriate component for processing. It acts as a mediator between the user and the other components, ensuring that queries are executed correctly and quickly.

The Optimization Engines are responsible for optimizing the SQL query. They analyze the query and determine the most efficient way to execute it. This involves selecting the best indexes, creating optimal execution plans, and choosing the most efficient join algorithms. Optimization engines use complex algorithms and statistical models to ensure that SQL queries are executed as efficiently as possible.

The Classic Query Engine allows data professionals and users to maintain non-SQL queries. It acts as an interface between the SQL query and the underlying database. This component translates the SQL query into a format that the database can understand and execute. It is responsible for managing the data structures, indexes, and access methods used by the database.

Finally, the SQL Query Engine is responsible for executing the SQL query. It receives the optimized query from the optimization engines and passes it on to the classic query engine. The SQL query engine then retrieves the data from the database and returns it to the user.

The architecture of SQL is shown in the diagram below:


As you can see, the Query Dispatcher receives the SQL query and passes it on to the Optimization Engines. The Optimization Engines then optimize the query and pass it on to the Classic Query Engine. The Classic Query Engine translates the query into a format that the database can understand and executes it. Finally, the SQL Query Engine retrieves the data from the database and returns it to the user.

In conclusion, SQL is a powerful and essential tool for managing and manipulating relational databases. Its four components work together to ensure that SQL queries are executed efficiently and effectively. By understanding the role of each component in the SQL process, data professionals and users can optimize their SQL queries and ensure that their databases operate smoothly and efficiently.

Some SQL Commands

SQL has a large set of commands that allow users to perform various operations on databases. Here are some of the most commonly used commands:

  • SELECT: Retrieves data from one or more tables
  • INSERT: Adds new data to a table
  • UPDATE: Modifies existing data in a table
  • DELETE: Removes data from a table
  • CREATE: Creates a new database or table
  • ALTER: Modifies the structure of an existing database or table
  • DROP: Deletes a database or table
  • JOIN: Combines data from multiple tables into a single result set


SQL is a relational database management system, while No-SQL (Not only SQL) databases are non-relational databases. No-SQL databases use a variety of data models for storing and retrieving data, such as document-oriented, key-value, and graph databases. While SQL databases are typically used for transactional data, No-SQL databases are often used for big data and real-time applications.


Here is a tabular comparison between SQL and NoSQL databases:

Feature SQL NoSQL
Data Model Relational Non-relational
Schema Predefined schema Dynamic schema
Query Language SQL Proprietary query language (if any)
Scalability Vertical scaling required Horizontal scaling required
ACID Compliance Fully ACID compliant Some NoSQL databases are not fully ACID compliant
Data Consistency Strong consistency Eventual consistency or weak consistency depending on the database
Data Integrity High data integrity May sacrifice data integrity for scalability and performance
Data Structure Structured data stored in tables Semi-structured or unstructured data
Data Storage Typically stored on disk Can be stored on disk or in-memory
Use Cases Best suited for complex transactions and heavy data loads Best suited for big data and high-velocity data streams

In summary, SQL databases are best suited for applications that require strong data consistency, high data integrity, and complex transactions. NoSQL databases, on the other hand, are ideal for handling large volumes of unstructured or semi-structured data, and for applications that require high scalability and performance. The choice between SQL and NoSQL depends on the specific needs and requirements of the application.

Advantages of SQL

  • Easy to learn and use
  • Supports complex queries for retrieving specific data from large databases
  • Offers a standardized way to manage and manipulate data in relational databases
  • Provides strong data consistency and integrity
  • Offers robust security features to protect data from unauthorized access

Disadvantages of SQL

  • Limited scalability for very large databases
  • Requires structured data to work effectively
  • May not be suitable for unstructured or semi-structured data
  • May not be the best choice for real-time or high-performance applications.

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