The study of SQL S2 semester

Chapter I.

Design of the database

A good database design

1

, save the database storage space

2

, to ensure the integrity of the data

3

, facilitate the development of database application system

Poor database design

1

, low efficiency

2

, updating, and retrieving data, there are many problems

Steps to design a database

1

, demand analysis phase

Analyze customer's business and data processing needs

⑴

Collect information

⑵

Identifying objects

(

Entity

)

⑶

Identify the details that each object needs to store

⑷

Identify the relationships between objects

2

, Outline design phase

Drawing the Database

E-r

Model Diagram

(

Entity Relationship Diagram

)

3

, Detailed design phase

Will

E-r

Graph converted to multiple tables

,

Make a logical design

,

and apply the three major specifications of database design into

Line Design

4

, Code authoring phase

Map cardinality

1

One

2

One-to-many

3

Many-to-one

4

Many-to-many

Entity Relationship Diagram

Rectangles represent entity sets

Ellipse Representation Property

Diamond represents a relationship set

Straight lines are used to connect

Designing Database Problems

1

Information duplication

2

Update exception

3

Insert exception

(

Unable to represent certain information

)

4

Delete exception

(

Loss of useful information

)

Three normative theories of database design

One

The objective of the first paradigm is to ensure that

The atomicity of each column

Two

The objective of the second paradigm is to ensure that

Each column in the table is associated with the primary key

Three

The objective of the third paradigm is to ensure that

Each column is directly related to the primary key

,

Rather than indirectly related

(

Cannot pass dependent

)

The relationship between normalization and performance

In case of necessity

Allow appropriate data redundancy

The study of SQL S2 semester