Struture Query Languages

Q . Explain the ERD and give examples of tables and how they are related

ERD stands for Entity Relationship Diagram . It is a diagram which is used to express the structure of the database logically . Often , making Entity Relation Diagram is the first step when designing a software application or a web application

Entities , attributes and relationships are represented in entity relationship diagram through different shapes

Rectangles , represent entity sets

Ellipses , represent attributes

Diamonds , represent relationship sets

Lines , represent linking attributes to entity sets and entity sets to relationship

sets

This is basic entity relationship diagram . For example in this diagram the two attributes on the top left belong to a single entity (which is represented in rectangle . Entities have relations between each other There can be different type of relationships

one to many relationship (for example , a teacher is related to many students

one to one relationship ( for example , one person can only have one Facebook account

many to many relationship ( for example , many people can talk to many salesman in a shopping mall

Q . Describe entities , attributes , primary keys , foreign keys , and defining relationships , highlighting their differences . Give some examples

Entity is a single person , place , or thing about which data can be stored . For example , a student has student number , student name address , phone number , and so on . All of these details together is placed in the single entity or table called student . The entities may have relationship between the entities . For example , student entity may have...