Database optimization ER model design .

If your company is one of those CEOs who often come to see it, this design can quickly query the required information, but if you manage it yourself, I think, put"Contact"with"Correspondence units"Synthesize a table, change the field of the correspondence unit to the contact, and use SQL to quickly find it if you want to query the correspondence unit or something separately; Combine the inventory information and ** information into a table; The table on the left is pretty much the same, but there are some fields that you can adjust yourself, depending on your situation, I hope it can help

The ER data model is generally used in the conceptual structure design phase of database design. The ER model is commonly used in information system design; For example, they are used in the conceptual structure design phase to describe the information requirements or the type of information to be stored in the database.

However, data modeling techniques can be used to describe any ontology (i.e., an overview and categorization of the terms used and their connections) for a particular domain (i.e., the region of interest). In the case of database-based information system design, in a later stage (often called logical design), the conceptual model is mapped to a logical model such as a relational model; It is in turn mapped to the physical model during physical design. Note that sometimes these two phases are referred to together as "physical design".

The ER diagram is a conceptual model and is not tied to a specific DBMS.

Judging from your screenshot, the database model diagram mentioned in the screenshot is inaccurate, and the correct one is that the ER model is converted to a relational model.

Since the ER diagram belongs to the conceptual design stage, its next stage is to convert it into a relational model, which is related to the specific DBMS.

Here are the common four phases of database design:

The first stage: user demand analysis;

Phase 2: Conceptual design (i.e. e-r model); The third stage is not tied to the specific DBMS: the relational model; The fourth stage, the physical model, is related to the specific DBMS.

The ER model is a conceptual model that reflects the database application system, and there are many ways to represent the conceptual model, the most commonly used of which is the E-R model, which was proposed in 1976 and is the entity-contact model in Chinese.

The conceptual data model is a user-facing, real-world data model that is independent of DBMS. It is primarily used to describe the conceptual structure of a unit.

Using the conceptual data model, database designers can focus on understanding and describing the real world at the beginning of the design phase, and postpone some of the technical issues involving the DBMS until the design phase.

The ER model can reflect the relational model of the database application system.

The transformation from the ER model to the relational model is to further organize the abstract data, and after the conversion is completed, the data can be displayed in the form of two-dimensional **, which is beneficial to store the data in the database. Database our operations on data.

The ER model is a method, a tool for people to understand the objective world. The relational model is a product of translating the ER model into the DBMS world. They are designed to continuously meet the needs of the user.

The ER model is composed of entities and connections, entities are abstractions in real life, and information transmission between entities is realized through connections. An attribute is a business card that an entity shares with a contact. In terms of classification, there are simple attributes and composite attributes, single-valued attributes and multi-valued attributes, stored attributes and derived attributes.

The operation of the ER model is actually the operation of the elements of the ER model, that is, the operation between entities, connections, and attributes, and the purpose of the operation is to meet the needs of users while reducing data redundancy.

ER model of the database.

ER model (entity relationship model) is a conceptual data model that describes data and its connection, and is a powerful tool for database application system designers and ordinary non-computer professional users to model and communicate and exchange, which is very intuitive and easy to understand, simple and easy to use. Then establish a logical data model and a physical data model that are compatible with the computer database management system, and finally install, height and run the database on the computer system.

The basic building blocks in the ER model.

The ER model is a method of graphically representing data and its connections, using graphical components such as rectangles, diamonds, ellipses, and connecting lines.

The rectangle represents the entity, and the name of the entity is written in the rectangular box;

The diamond shape indicates the connection, and the contact name is written in the diamond box;

The ellipse represents the property, and the name of the property is written in the elliptical box;

Connection lines represent the affiliation between entities, connections, and attributes, or the connection between entities and connections.

It's the conceptual model design phase

The conceptual model does not depend on a specific computer system, it is a conceptual structure that purely reflects the information needs.

Modeling is based on the results of requirements analysis, and often abstracts the data. Common methods of data abstraction are 'aggregation' and 'generalization'.

The ER method is commonly used when designing conceptual models. The designed ER diagram and the corresponding instructions can be used as stage results.

Conceptual model design can be done in three steps.

Design a local conceptual model].

Determine the scope of the local conceptual model.

Define entities. Define the connection.

Determine the attributes. Draw all the local ER diagrams one by one, and attach the corresponding explanatory file [Design Global Conceptual Model].

The steps to create a global ER diagram are as follows:

Determine the type of public entity.

Merge local ER diagrams.

Eliminate inconsistencies.

Optimized the global ER chart.

Draw a global ER diagram and attach the corresponding documentation.

Review of the conceptual model].

The review of the conceptual model was conducted in two parts:

The first part is the user review.

The second part is the developer review.

The e-r model is the entity-relational model and the database.

Design Concept Design Tasks

The next step of conceptual design is to produce the logical design of the relationship model, the normalization of the relationship model is also applied at this time, and according to the conversion method from the E-R model to the relationship model, all the relationship patterns can generally be obtained, but the results of the logical design are not only.

First, in order to further improve the performance of the database application system, the structure of the data model should be appropriately modified and adjusted according to the requirements, and the normalization theory is introduced at this time.

Therefore, I think that the E-R model only abstracts the real-world information into conceptual information, and then transforms it into a relational model, and the resulting relational model is not perfect, it should only conform to the first normal form, but through the standardized optimization of logical design, it should be able to reach the third normal form at the minimum.

Without the first normal, there is no third normal, but the relational patterns designed in our application must be able to achieve 3nf.

Let's choose A.

set field = (select replace(field +.)'.jpg',' ','') from table a where aPrimary key field = table

Conceptual structure design, logical structure design, physical structure design.

Microsoft Office Visio makes it easy to design a database ER model.

It's not difficult, just find the right entity and relationship.