some SQL Questions i need help on Question 1: Define the term entity and give an

Question

some SQL Questions i need help on

Question 1: Define the term entity and give an example other than those used in this book.

Question 2: Define the term attribute and give examples for the entity you described in question 1.

Question 3: Define the term identifier, and indicate which attribute defined in your answer to question 2 identifies the entity.

Question 4: Define the term relationship and give an example other than those used in this book.

Question 5: List and give an example of the three types of binary relationships other than the ones used in this book. Draw a traditional E-R diagram for each. Follow the formats shown in Figure 4-5.

Explanation / Answer

Hi, I have answered Q1,2 and 3.

Please repost others in separate post.

Definition of an Entity
An entity is a database object that represents a thing in the real world. Entities are expressed as nouns.
Entities can be concrete, like buildings and employees or they can be more abstract things like departments and accounts.

Ex: "John", "CSE305"

Attribute: describes one aspect of an entity type; usually [and best when] single valued and indivisible (atomic)
Represented by oval on E-R diagram
Ex: Lets Person is an Entity type and attributes of Person are name, id

An identifier is the representation within the language of items created by the user, as opposed to language keywords or commands. Some identifiers stand for dictionary objects, which are the objects you create- such as tables, views, indexes, columns, and constraints- that are stored in a database. They are called dictionary objects because Derby stores information about them in the system tables, sometimes known as a data dictionary. SQL also defines ways to alias these objects within certain statements.

SELECT P.name
FROM Person P; // here P is an identifier

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