SQL Intro

In this today's technology there has been a growing demand for SQL. SQL developers are in high demand across a wide range of industries, from health care to retail to finance.

       Now before Comming to sql ; first we have to know what is DBMS 

* DBMS - Data Base Management System 

    (A Software designed to store define retrieve and manage data in database)

* Database- A database is a collection of interrelated data and information e.x.

  

NAME	ROLL	DOB	EMAIL	ADDRESS
OJAS	11	03-04-2000	ojas@gmail.com	CHENNAI
TEJAS	16	07-09-2002	tejas@gmail.com	UP

              Advantages of Dbms 

1.   Data Sharing → File system doesn't  allow sharing of data or sharing is too complex.Where as in DBMS, data can be shared easily due to centralized system.

2. Data Integrity →There may be cases when some constraint's need to be applied on the data before inserting it in database.The file system doesn't provide any procedre to check these constraint's automatically.Where as dbms maintain integrity  by enforcing user defined constraints on data by itself.

3.Data Redundancy and Inconsistency →Redundancy is the concept of repetition of data i.e. each data may have more than a single copy.The file system cannot  control redundancy of data .

                     Data abstraction in dbms 

→ Hide irrelevant details from the users.This approach simplifies database design. 

   There are mainly 3 levels of data abstraction ➗

i.  Physical →This is lowest level of data abstraction.It tells how the data is actually in memory 

ii.  Logical →This level comprises the information that is actually stored in the database in the form of tables.It also stores the relationship among the data entities in relatively simple structures.

iii .view→This is the highest level of abstraction only a part of the actual database is viewed by user.

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