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Introduction to SQL
Wha is it?
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Short for Structured Query Language
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Sometime pronounce as the sequel.
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SQL is a standard language for storing, manipulating and retrieving data in databases.
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Microsoft SQL Server, MySQL, Oracle, Firebird SQL, PostgreSQL etc use SQL for querying with slight syntax differences.
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SQL is a greater tool with web languages such as PHP, Python, Java, ASP etc to build dynamic web applications.
SQL Commands
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SQL commands are instructions, coded into SQL statements.
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These are used to communicate with the database to perform specific tasks, work, functions, and queries with data.
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It is a very powerful and diverse database language use for storing data into databases.
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SQL is not case sensitive.
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But SQL Data is a case sensitive.
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Some database systems require a semicolon at the end of each SQL statement
Types of SQL Statements
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SQL statements are divided into four main categories:
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DML - Data Manipulation Language
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DDL - Data Definition Language
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DCL - Data Control Language
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TCL - Transaction Control Language
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SCL - Session Contol Language
SQL Language Staements
DML
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SELECT
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INSERT
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UPDATE
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DELETE
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MEGE
DDL
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CREATE
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ALTER
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DROP
DCL
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GRANT
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REVOKE
TCL
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BEGIN
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TRAN
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COMMIT
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ROLLBACK
SCL
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SET ROLE
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ALTER SESSION
DML
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Data manipulation statement is used for managing data within table object.
DDL
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Data definition statement are used to define the database structure or table.
DCL
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Data control statement are use to give privileges to access limited data.
TCL
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Transaction control statement are use to apply the changes permanently save into database.
SCL
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Session control statement are manage properties dynamically of a user session.
History
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Developed in 1970.
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By Raymond and Donald Chamberlin at IBM.
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Commercially released by Relational Software Inc.
Why SQL
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Relational databases use GUIs for easier database management, and queries can now be simplified with graphical tools, e.g., drag-and-drop wizards.
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However, learning SQL is imperative because such tools are never as powerful as SQL.
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