SQL Introduction

SQL stands for Structured Query Language(or SEQUEL-Structured English Query Language). SQL
is use for accessing and manipulating databases.SQL is not case sensitive but SQL Data is a case sensitive.

SQL was developed by IBM Corporation.
SQL became an ANSI standard, called SQL-87, in 1986.
ISO made a major revision, called SQL-92, in 1992.
The latest revision is SQL:2008.

Before starting SQL, relational databases have several point that are important to keep in mind.

• RDBMS stands for Relational Database Management System.
• Data Integrity : Store data only once and avoiding data duplication.
• SQL Constraints : Constraints are the rules which are apply to table columns to store valid data and prevents the user to storing/entering invalid data into table columns.
• Better security : Assign grant or privilege to a individual User. Using this grant user can store confidential data into table by using username or password.
• Database Normalization : Database normalization is the process to store database data very efficiently. No need to store same data more then one time and reduce the Data redundancy.
• Different types of relationships : One to one, One to many, Many to many

                One to one relationship : merging for two tables.
                One to many relationship : create a foreign key from an parent table to the child table.
                Many to many relationship : create a new relation table.


Rules of Semicolon(;) or Forward Slash(/) in SQL

There is a huge difference in SQL between the meaning of a (/) and a (;) because they work differently.

SQL database systems require semicolon(;) at the end of statement to know it's ending.
Use forward slash(/) once at the end of each script, to tell SQL that there is not more lines of code. you can't use forward slash(/) at the middle of the script.
The (;) means terminate the current statement execute it and store it to the "SQL buffer", whereas the / executes whatever statement script is in the current "SQL buffer".