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Introduction to SQL

Introduction to SQL

SQL is a standard language for accessing and manipulating databases.

What is SQL?

  • SQL stands for Structured Query Language
  • SQL lets you access and manipulate databases
  • SQL is an ANSI (American National Standards Institute) standard

What Can SQL do?

  • SQL can execute queries against a database
  • SQL can retrieve data from a database
  • SQL can insert records in a database
  • SQL can update records in a database
  • SQL can delete records from a database
  • SQL can create new databases
  • SQL can create new tables in a database
  • SQL can create stored procedures in a database
  • SQL can create views in a database
  • SQL can set permissions on tables, procedures, and views

Some of The Most Important SQL Commands

  • SELECT - extracts data from a database
  • UPDATE - updates data in a database
  • DELETE - deletes data from a database
  • INSERT INTO - inserts new data into a database
  • CREATE DATABASE - creates a new database
  • ALTER DATABASE - modifies a database
  • CREATE TABLE - creates a new table
  • ALTER TABLE - modifies a table
  • DROP TABLE - deletes a table
  • CREATE INDEX - creates an index (search key)
  • DROP INDEX - deletes an index

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.

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 −
  • Query Dispatcher
  • Optimization Engines
  • Classic Query Engine
  • SQL Query Engine, etc
A classic query engine handles all the non-SQL queries, but a SQL query engine won't handle logical files.

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