SQL -- OVERVIEW
What is
SQL?
SQL is a language of database, it
includes database creation, deletion, fetching rows and modifying rows etc.SQL is
Structured Query Language, which is a computer language for storing,
manipulating and retrieving data stored in
relational database. SQL is the
standard language for Relation Database System. All relational database
management systems like MySQL, MS Access,
Oracle, Sybase, Informix, postgres and SQL Server use SQL as standard database language. Also, they are using different dialects,
such as: MS SQL Server using T-SQL,Oracle using PL/SQL, MS Access version of
SQL is called JET SQL native format etc.
Why SQL?
ü
Allows users
to access data in relational database management systems.
ü
Allows users
to describe the data.
ü
Allows to
embed within other languages using SQL modules, libraries & pre-compilers.
ü
Allows users
to create and drop databases and tables.
ü
Allows users
to create view, stored procedure, functions in a database.
ü
Allows users
to set permissions on tables, procedures, and views
ü
Allows users
to define the data in database and manipulate that data.
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 and its later becoming
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 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.
SQL Commands:
The standard
SQL commands are CREATE, SELECT,
INSERT,UPDATE, DELETE and DROP. These commands can be classified into three groups
DDL - Data
Definition Language
|
|
CREATE
|
CREATE Creates a new table, a view of a table, or
other object in database
|
ALTER
|
ALTER Modifies an existing database object, such
as a table.
|
DROP
|
DROP Deletes an entire table, a view of a table
or other object in the
database
|
DML - Data
Manipulation Language
|
|
SELECT
|
SELECT Retrieves certain records from one or more
tables
|
INSERT
|
INSERT Creates a record
|
UPDATE
|
UPDATE Modifies records
|
DELETE
|
DELETE Deletes records
|
DCL - Data
Control Language
|
|
GRANT
|
GRANT Gives a privilege to user
|
REVOKE
|
REVOKE Takes back privileges granted from user
|
