SQL-Tutorials/README.md

SQL-Tutorials ❤️

In this module, I will be updating the topic wise SQL tutorial notes which is very useful for a fresher to start with MYSQL from basics

Introduction 👋

• SQL stands for Structured Query Language.
• This tutorial will give you a quick start to SQL.
• It covers most of the topics required for a basic understanding of SQL and to get a feel of how it works.

A Brief History of SQL ⌚

1970 − Dr. Edgar F. "Ted" Codd of IBM is known as the father of relational databases. He described a relational model for databases.

1974 − Structured Query Language appeared.

1978 − IBM worked to develop Codd's ideas and released a product named System/R.

1986 − IBM developed the first prototype of relational database and standardized by ANSI. The first relational database was released by Relational Software which later came to be known as Oracle.

Why to Learn SQL 🤔

• SQL is the standard language for Relational Database System.
• All the Relational Database Management Systems (RDMS) like MySQL, MS Access, Oracle, Sybase, Informix, Postgres and SQL Server use SQL as their standard database language.

Also, they are using different dialects, such as −

1) MS SQL Server using T-SQL,

2) Oracle using PL/SQL,

3) MS Access version of SQL is called JET SQL (native format) etc.

Applications of SQL ✔️

• SQL is one of the most widely used query language over the databases.
• I'm going to list few of them here:

- Allows users to access data in the relational database management systems.

- Allows users to describe the data.

- Allows users to define the data in a database and manipulate that data.

- Allows to embed within other languages using SQL modules, libraries & pre-compilers.

- Allows users to create and drop databases and tables.

- Allows users to create view, stored procedure, functions in a database.

- Allows users to set permissions on tables, procedures and views.

SQL Process ⌛

• When you are executing an SQL command for any RDBMS, the system determines the best way to carry out your request and SQL engine figures out how to interpret the task.
• There are various components included in this process. These components are −

1) Query Dispatcher

2) Optimization Engines

3) Classic Query Engine

4) SQL Query Engine, etc.

5) A classic query engine handles all the non-SQL queries, but a SQL query engine won't handle logical files.

SQL Commands 📌

• The standard SQL commands to interact with relational databases are CREATE, SELECT, INSERT, UPDATE, DELETE and DROP.
• These commands can be classified into the following groups based on their nature −

DDL - Data Definition Language 😀

CREATE

• Creates a new table, a view of a table, or other object in the database.

ALTER

• Modifies an existing database object, such as a table.

DROP

• Deletes an entire table, a view of a table or other objects in the database.

DML - Data Manipulation Language 😀

INSERT

• Creates a record.

UPDATE

= Modifies records.

DELETE

• Deletes records.

DCL - Data Control Language 😀

GRANT

• Gives a privilege to user.

REVOKE

• Takes back privileges granted from user.

TCL - Transaction Control Language 😀

COMMIT

• Save all the transactions to the database.

ROLLBACK

• Undo transactions that have not already been saved to the database.

SAVEPOINT

• Roll the transaction back to a certain point without rolling back the entire transaction.

Data Query Language 😀

SELECT

• select the attribute based on the condition described by WHERE clause.

RDBMS ⌛

• RDBMS stands for Relational Database Management System.
• RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
• A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd.

Tables 🎰

• The data in an RDBMS is stored in database objects which are called as tables.
• This table is basically a collection of related data entries and it consists of numerous columns and rows.

Field 🎯

• Every table is broken up into smaller entities called fields.
• The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.
• A field is a column in a table that is designed to maintain specific information about every record in the table.

Record 🎲

• A record is also called as a row of data is each individual entry that exists in a table.

Column 🏹

• A column is a vertical entity in a table that contains all information associated with a specific field in a table.

NULL value 🚫

• A NULL value in a table is a value in a field that appears to be blank, which means a field with a NULL value is a field with no value.
• It is very important to understand that a NULL value is different than a zero value or a field that contains spaces.
• A field with a NULL value is the one that has been left blank during a record creation.