SQL

What is SQL?

SQL is Structured Query Language, which is a computer language for storing, manipulating, and retrieving data stored in a relational database.

SQL is the standard language for Relational Database systems. 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 −

• Oracle using PL/SQL,
• MS Access version of SQL is called JET SQL (native format) etc.

Why SQL?

SQL is widely popular because it offers the following advantages −

• 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 embedding within other languages using SQL modules, libraries & pre-compilers.
• Allows users to create and drop databases and tables.
• Allows users to create views, store procedures, and functions in a database.
• Allows users to set permissions on tables, procedures, and views.

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 a relational database and standardized it 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 the 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.

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

SELECT : Retrieves certain records from one or more tables.

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.