SQL - Overview

SQL (Structured Query Language) is used to modify and access data or information from a storage area called database. This beginner online training sql tutorial website teaches you the basics of SQL code and train you how to write & program SQL queries. I will be sharing my database knowledge on SQL and help you learn programming SQL better.
The concepts discussed in this SQL tutorial can be applied to most of database systems. The SQL syntax used to explain the tutorial concepts is similar to the one used in Oracle database.

What is SQL

  • SQL stands for Structured Query Language.
  • It is designed for managing data in a relational database management system (RDBMS).
  • It is pronounced as S-Q-L or sometime See-Qwell.
  • SQL is a database language, it is used for database creation, deletion, fetching rows and modifying rows etc.
  • SQL depends on relational algebra and tuple relational calculus.
All DBMS like MySQL, Oracle, MS Access, Sybase, Informix, Postgres and SQL Server use SQL as standard database language.


Why SQL?


  • Allows users to access data in relational database management systems.
  • Allows users to describe the data.
  • Allows users to define the data in 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 the process. These components are Query Dispatcher, Optimization Engines, Classic Query Engine and SQL Query Engine, etc. Classic query engine handles all non-SQL queries but SQL query engine won't handle logical files.

Following is a simple diagram showing SQL Architecture:

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 groups based on their nature:

DDL - Data Definition Language:

CommandDescription
CREATECreates a new table, a view of a table, or other object in database
ALTERModifies an existing database object, such as a table.
DROPDeletes an entire table, a view of a table or other object in the database.

DML - Data Manipulation Language:

CommandDescription
SELECTRetrieves certain records from one or more tables
INSERTCreates a record
UPDATEModifies records
DELETEDeletes records

DCL - Data Control Language:

CommandDescription
GRANTGives a privilege to user
REVOKETakes back privileges granted from user



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