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The basic concept of database

A database is a warehouse that organizes, stores and manages data according to the data structure. It is a collection of organized, shareable and uniformly managed large amounts of data stored in a computer for a long time. A database is a collection of data stored together in a certain way, shared with multiple users, with as little redundancy as possible, and independent of the application. It can be regarded as an electronic filing cabinet-a place where electronic files are stored. Users can add, query, update, delete and other operations on the data in the file.

data

Symbolic records that describe things are called ishuju (Data), including numbers, text, graphics, images, sounds, archival records, etc., stored in a unified format in the form of "records".

Tables organize different records together to form a "table" that is used to store specific data.

A database database is a collection of tables, which is the interrelated data stored in the warehouse where the database is stored in a certain organizational way.

Database introduction

A relational database that represents a symbolic record that describes things

Write SQL rules, query accounts for 2/3, modification accounts for 1/3

The role of database: persistent preservation of data, high reliability, high availability, fast data extraction

According to the storage type, the database is divided into relational database and non-relational database.

Relational database: stores numeric values, characters, strings, Boolean values, etc.

Non-relational database: stores pictures, videos, voice, etc.

Relational databases: mysql (belonging to oracle), sql server (Microsoft), access (Microsoft office), oracle (oracle), db2 (IBM), sybase (sybase), etc.

Sql server high-performance concurrency is very low, low stability, including value-added services.

The Inland Revenue Department uses oracle

Customs uses oracle.

The State Grid uses db2, and the operation is irreversible.

Sybase can withstand hundreds of millions of concurrency.

Non-relational database (collectively referred to as NOSQL)

MongoDB, redis (in-memory database, where data is stored in memory, also known as cache database), memcache (also memory database / cache database, and KV key-value pair storage)

What redis and memcache have in common: both can store hot databases (databases that are often used repeatedly)

The difference: redis can be persisted and objects can be stored.

Development history of database system

In the history of the development of the database, the database has experienced various stages of development, such as hierarchical database, mesh database and relational database, and the rapid development of database technology in all aspects. In particular, relational database has become the most important member of database products at present. since the 1980s, almost all the new database products of database manufacturers support relational database. even some non-relational database products almost have interfaces to support relational databases. This is mainly because the traditional relational database can better solve the problem of managing and storing relational data. With the development of cloud computing and the arrival of big data era, relational database is more and more unable to meet the needs, mainly because more and more semi-relational and non-relational data need to be stored and managed by database, at the same time, the emergence of new technologies such as distributed technology also puts forward new requirements for database technology, so more and more non-relational databases begin to appear. This kind of database is very different from the traditional relational database in design and data structure. They put more emphasis on the high concurrent reading and writing of database data and the storage of big data. This kind of database is generally called NoSQL (Not only SQL) database. However, the traditional relational database still maintains a strong vitality in some traditional fields.

First generation database

Since the 1960s, the first generation of database system has come out. They are the database system of hierarchical model and mesh model, which provides a strong support for unified management and sharing of data.

The second generation database in the early 1970s, the second generation database-relational database began to appear. In the early 1980s, IBM's relational database system DB2 came out. As the relational database of the second generation database system, it began to gradually replace the database of hierarchical and network model, and became the dominant database and the mainstream of the industry. Up to now, relational database system still occupies the main position of database application.

Since the 1980s, a variety of new database systems adapted to different fields have been emerging, such as engineering database, multimedia database, graphic database, only database, distributed database and object-oriented database, especially the object-oriented database system, which is favored by people in the late 1990s because of its strong practicability and wide adaptability. Formed a variety of database systems to support the application of the situation. Of course, in business applications, relational databases still dominate, but some new elements have been added to the mainstream business database systems. For example, the "relational-object" database model supported by Oracle.

SQL Server (Microsoft products) is introduced in today's mainstream database.

Oriented Windows operating system Oracle (Oracle products)

For all mainstream platforms

Safe, perfect, complex operation DB2 (IBM products)

For all mainstream platforms

Large, secure, perfect MySQL (acquired by Oracle)

Free, open source, small size

Relational database

Overview

The relational database system is a database system based on the relational model. Its basic concept comes from the relational model. The relational model is based on the theory of relational algebra. The data structure uses an easy-to-understand two-dimensional data table, and a simple "entity-relation" diagram can be used to directly represent the Emure R diagram, which contains three elements: entities (data objects), relations and attributes.

Entity

Also known as an example, corresponding to "events" or "things" that can be distinguished from other objects in the real world, such as bank customers, bank accounts, etc.

Attribute

A characteristic of an entity that an entity can have more than one attribute. For example, each entity in the "bank customer" entity set has attributes such as name, address, phone number, etc.

contact

The correspondence between entity sets is called a relationship, also known as a relationship. For example, there is a "savings" relationship between bank customers and bank accounts.

Application of relational database

Oracle,MySQL,SQLServer, Sybase,Informix, access,DB2 and FoxPRO are all relational databases.

Non-relational database key-value mode (kye-value), storing, deleting and modifying data column storage (Column--oriented) based on keys, storing related data in column groups as documents, the database is composed of a series of data items, each data item has a name and a corresponding value graphic mode, the entity is the vertex, the relationship is the edge, and the data is saved as a graph.

MySQL database

Summary MySQL is a popular open source relational database Oracle products that follow the GPL agreement and can be used and modified free of charge

It features excellent performance, stable open source service, no copyright restrictions, low cost, multithreading, and multi-user security and reliability based on Chand S (client / server) architecture.

Mysql Business Edition and Community Edition

Mysql Business Edition is developed and maintained by MySQL ab and can only be used for a fee.

Mysql Community Edition is developed and maintained by Mysqk developers and enthusiasts scattered around the world and can be used free of charge.

The difference between the two is more stringent in the organization, management and testing of the commercial version. If the commercial version does not comply with GPL, you can get 24-hour service, such as fault maintenance and patching, etc.

MySQL product camp

The first camp: camp 5.0 Murray 5.1, which can be said to be the continuation of the early products. The second camp: Camp 5.4 Murray 5.7, which better integrates the storage engines developed by Mysql AB, the community and third-party companies to improve performance. The third camp: camp 6.0 Murray 7.1, that is, the MySQL Cluster version. Develop MySQL to meet the database needs of the new era cluster. Download address: http://www.dev.mysql.com/downloads

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