SQL Server - Part 1

SQL is commonly called as Simple Query Language. When computer came to be, people started keep tracks of files which called as databases.

Entity - 

Entity is a thing which is a representation of real world object. Each row in a table represents an single entity and column represent attributes of an entity. In an entity you should keep track only on essential attributes to your need. A table holds only one kind of entity.


Primary Key -

Entity which represents a real world item is unique. It should appear on the table once. This uniqueness of an object in real world is created by its' attributes.
            eg :- I saw a red Porche car on Temple road.
                    A policeman gave a parking ticket ADCS235456423.

So to identify the same object different users use different attributes. The attributes to identify the object is chosen according to the purpose.

Scalar Values -

Scalar values are whole numbers we use to count.
eg :- -12,-45,0,3,65,23

Numbers which are used to indicate a point in 2D and 3D are not considered as scalar values. But date can be considered as a scalar value because you can sort date in a way that would give a sense of meaning.

RDBMS (Relational DataBase Management System)

RDBMS is an application running on a server. It maintains access control to database files. To modify,create or delete a database file in RDBMS, we use a text specific language which is passed from client to server through many networking protocols.
If there are two applications trying to access a same file simultaneously then there might be a problem arising. When we have this kind of a situation, RDBMS maintain a traffic cop. The purpose of RDBMS is to protect and serve the data stores.