This repository is divided into following subfolders, where each folder contains different topics related to Query language, Databases, Data warehouse, data lake, and about some tools (MySQL, PostgreSQL, Bigquery, Snowflake, Apache airflow etc.). In the end of the Repository, I have also given some simple example projects.

• 1.0-Query-language: This contains the basic query based language
• 2.0-BigQuery: Fundamentals of GCP Bigquery
• 3.0-PostgreSQL: Fundamentals of GCP Bigquery & a example
• 4.0-Database: Databases, Data warehouse, Data lake, Data pipline on Snoflake and Airflow at AWS
• 5.0-SQL-tutorials: ABout SQL in details
• 6.0-Project: Projects

1. An introduction to SQL: a beginner's guide

• Query Languages (QL)
• Important Query languages
• What is SQL?
• Need for SQL
• Some of the advantages of SQL
• Disadvantages of SQL
• SQL (Relational) and NoSQL
• MySQL and BigQuery

2. What is Data?

• Role of data in a program
• Data categories

3. What is a Database?
   • Database Model
   • What is DBMS?
   • DBMS categories
4. What is a Relational Database?
5. SQL Commands, explained

<ul>
    <li> SQL is a domain-specific programming language that is used to manage relational databases.</li>
    <li> It is designed for managing and querying data that is organized in a relational database management system (RDBMS).</li>
    <li> SQL provides a standardized way to perform various database operations such as creating, modifying, and deleting database tables, inserting, updating, and deleting data in tables, and querying the database to retrieve specific information.</li>
    <li> SQL is used by a wide range of organizations to manage and analyze data stored in databases.</li>
    <li> It is a fundamental tool for data analysts, database administrators, software developers, and other professionals who work with data in relational databases.</li>
</ul>

But Going into more details on SQL, first lets know what are main query languages used, what are database and understand differences between few terminology.

• QL is a general term used to describe a variety of query languages used in database management systems (DBMS).
• These query languages are used to interact with the database, allowing users to search, retrieve, and modify data stored within the system.

There are numerous Query Languages (QL) used in database management systems (DBMS). Some of the most common QLs include:

1. SQL (Structured Query Language) - used to communicate with relational databases.

2. XQuery - used to retrieve and manipulate data stored in XML documents.

3. SPARQL (SPARQL Protocol and RDF Query Language) - used to query and manipulate data stored in RDF databases.

4. Cypher - used to query graph databases.

5. Gremlin - used to traverse and manipulate graph data stored in graph databases.

6. MDX (Multidimensional Expressions) - used to query data stored in multidimensional databases.

7. Datalog - used to query and reason about data stored in deductive databases.

8. FQL (Facebook Query Language) - used to query data stored in Facebook's data infrastructure.

9. SOQL (Salesforce Object Query Language) - used to query data stored in Salesforce's customer relationship management (CRM) system.

10. OQL (Object Query Language) - used to query and manipulate data stored in object-oriented databases.

These are just a few examples of the many QLs used in database management systems.

"SQL stands for Structured Query Language".

• SQL is a computer language for storing, manipulating, and retrieving data in a relational database.
• SQL provides useful commands for performing these operations.

• Because of its popularity, multiple vendors started their own implementations of relational databases.
• The need to develop one common language for managing both data and structures became necessary.

• Easy to learn: SQL has a simple and easy-to-understand syntax, which makes it easy for beginners to learn.
• Portable: SQL is a standard language, which means that it can be used with a variety of relational database management systems (RDBMS).
• High performance: SQL is optimized for performance and can handle large amounts of data quickly and efficiently.
• Scalable: SQL databases can scale easily by adding more servers or increasing the resources of existing servers.
• Flexible: SQL can be used to perform a wide range of tasks, from simple queries to complex analytics and data mining.
• Secure: SQL includes built-in security features that can help protect against data breaches and unauthorized access.
• Ad-hoc querying: SQL allows users to run ad-hoc queries against their data, which can be useful for exploring data and finding insights.
• Data integrity: SQL databases include features such as transactions and constraints that help ensure the integrity of the data stored in the database.
• Ease of integration: SQL databases can be easily integrated with other applications and tools, making it easy to access and analyze data from different sources.
• Standardization: SQL is a standardized language, which means that developers can use the same language and code across different databases and platforms.

With the advantages of SQL, it also has some disadvantages, which are as follows:

• Complexity: SQL can be complex and difficult to learn, especially for those who are new to programming.
• Limited scalability: SQL databases can struggle with scalability when it comes to handling large volumes of data, especially when compared to NoSQL databases.
• Limited flexibility: SQL databases are designed to handle structured data, which means they may not be as flexible as NoSQL databases when it comes to handling unstructured or semi-structured data.
• Cost: SQL databases can be expensive, especially when using commercial database management systems.
• Security concerns: SQL databases can be vulnerable to SQL injection attacks, which can result in data loss or corruption.
• Performance issues: SQL databases can experience performance issues, especially when complex queries are involved. This can be exacerbated when dealing with large data sets.

MySQL and BigQuery are both relational database management systems (RDBMS), but they have several differences in terms of their architecture, functionality, and usage. Here are some of the key differences between MySQL and BigQuery:

1. Architecture: MySQL is a traditional client-server RDBMS, which means it is installed on a server and users connect to it using a client application. On the other hand, BigQuery is a cloud-based data warehouse, which means it is hosted on Google Cloud and accessed through a web interface or API.

2. Scalability: BigQuery is highly scalable and can handle petabytes of data, while MySQL is generally limited by the hardware it is installed on.

3. Query Language: Both systems use SQL as their query language, but BigQuery has some additional functions and features that are specifically designed for working with large datasets.

4. Cost: MySQL is open-source and free to use, while BigQuery is a paid service that charges based on the amount of data processed and storage used.

5. Use Cases: MySQL is often used for small to medium-sized applications that require a traditional RDBMS, while BigQuery is designed for large-scale data warehousing and analytics projects.

Overall, while both MySQL and BigQuery are RDBMS systems, they have different architectures, features, and use cases, and are often used for different types of projects.

Data are

• individual facts
• statistics
• items of information

All the programs can be divided into two major parts.

• Code (or algorithms)
• Data

The code in a program is static. But data is dynamic. Hence the runtime behavior of a program is largely dependent on data.

Data can be broadly categorized into 3 categories based on its format.

• Structured
• Unstructured
• Semi-Structured

Structured Data aka "Quantitative Data" is the data which

• has a well-defined structure
• conforms to a data model
• can be easily accessed and, used

Structured data accounts for only about 20% of data. Examples: Name, Address.

Unstructured Data aka "Qualitative Data" is the data which

• does not have any predefined data model
• cannot be processed by conventional tools

Unstructured data accounts for about 80% of data. Examples: Text Files, Audio/Videos.

• semi-structured data is the “bridge” between structured and unstructured data.
• It does not have a predefined data model and is more complex than structured data, yet easier to store than unstructured data.
• Mostly in JSON/XML/CSV formats.

A database is ❝an organized collection of data❞.

• stored in a computer system so that
• it can be easily accessed and managed

• A database model is a data model that determines the logical structure of a database.
• It fundamentally determines how data can be stored, organized, and manipulated.
• One popular database model is the relational model, which uses a table-based format.

DBMS stands for Database Management System.

• DBMS is the software that is used to manage a database (whereas a database is for storage).

• A DBMS interacts with

  • end users
  • applications
  • database

  A DBMS would typically take care of

  ❯ AuthN & AuthZ ❯ Create, Modify, Delete a Database ❯ Create, Modify, Delete Database Objects ❯ Create, Modify, Delete Data ❯ Query Data ❯ Handle transactions

• Broadly DBMS are categorized into
  • Relational DBMS (RDBMS)
  • NoSQL
• RDBMS handles relational models and manages structured data.
• NoSQL comes with various database models and manages both unstructured and semi-structured data.

A relational database is a ❝collection of data items❞ that have some ❝pre-defined relationships❞ between them.

These items are organized as a set of "Tables" with "Columns" and "Rows".

• A relationship between 2 tables is established based on one or multiple similar columns.

• DDL
• DML
• DQL
• DCL
• TCL

• DDL commands are used to define the database schema.
• DDL is a set of SQL commands that are used to create, modify, and delete database structures but not data.

• CREATE: Used to create the database or its objects (like Table, Views, Stored Procedures, Index, etc.)
• DROP: Used to delete objects from the database.
• ALTER: Used to alter the structure of the database.
• TRUNCATE: Used to remove all records from a table, including all spaces allocated for the records.
• RENAME: Used to rename an object already existing in the database.
• COMMENT: Used to add comments to the data dictionary.

• DML commands are used to manipulate the data present in the database.

• INSERT: Used to insert data into a table.
• UPDATE: Used to update existing data within a table.
• DELETE: Used to delete records from a database table.
• LOCK: Used to control the concurrency on a table.
• CALL: Used to call a PL/SQL code.
• EXPLAIN PLAN: To describe the access path to data.

• DQL commands are used for performing queries on the data within schema objects.

• SELECT: Used to retrieve data from the database.

• DCL commands mainly deal with the rights, permissions, and other controls of the database system.

• GRANT: To give users access privileges to the database.
• REVOKE: To withdraw the user’s access privileges.

• TCL commands deal with the transaction within the database.

• COMMIT: Used to commit a transaction.
• ROLLBACK: Used to rollback a transaction in case of any error occurs.
• SAVEPOINT: Used to set a savepoint within a transaction.
• SET TRANSACTION: Used to specify characteristics for the transaction.