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The basic concept of database

Symbolic records that describe things are called data.

Including numbers, text, graphics, images, sounds, archival records, etc.

To store in a uniform format in the form of a record

Each line record: OK

Each field-attribute-column forms the table

Table

A table is formed by organizing different records together.

Is used to store specific data.

A database is a combination of tables and a warehouse for storing data.

Interrelated data stored in a certain organizational manner

Development history of database system

First generation database

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

Second generation database

In the early 1970s, the second generation database-relational database began to appear.

In the early 1980s, DB2, the relational database of IBM Company, came out. As the relational database of the second generation database system, it began to be hierarchical and mesh model database step by step, becoming the dominant database and the mainstream of the industry. Up to now, relational database system still occupies the main position of database application.

The third generation database

Since the 1980s, a variety of new database systems have emerged to adapt to different fields, such as engineering database, multimedia database, graphic database, intelligent database, distributed database and object-oriented database, etc., especially the object-oriented database system is favored by people because of its strong practicability and wide adaptability.

In the late 1990s, a variety of database systems jointly supported applications were formed. Of course, in business applications, relational databases still occupy the mainstream. However, some new elements have been added to the mainstream business databases, but some new elements have been added to the business database system. For example, the relational-object database model supported by Oracle

Databases are divided into two categories.

Relational database data integer floating point character string (fixed length, variable length) Boolean value

Non-relational database objects (pictures, videos)

Introduction to today's mainstream databases

SQL Server Microsoft products

Oriented to Windows operating system

Simple and easy to use

Oracle Oracle products

For all mainstream platforms

Safe, perfect and complex to operate

DB2 IBM products

For all mainstream platforms

Large, safe, perfect

Acquisition by MySQL Oracle

Free, open source, small size

Relational database contains three elements: entities (data objects), relationships and attributes.

Relational database system is a database system based on relational model, and its basic concept comes from relational model.

Based on the theory of relational algebra, the data structure is expressed directly by a simple entity-relation diagram, which uses a two-dimensional data table that is easy to understand.

Entity

Also known as real list, 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 multiple attributes, such as bank customers, and each entity in the entity set has a name, address, telephone, and other attributes.

contact

The corresponding relationship between entity sets is called connection, also known as 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,FOXPRO

12306 user information system, Taobao account information system, website user information system are commonly used

Introduction to non-relational database

Non-relational databases, also known as NOSQL, do not store data based on relational models and do not require fixed table formats.

As a supplement to relational database, non-relational database plays an important role in high efficiency and high performance in the era of increasingly rapid development of websites.

Advantages of non-relational database

The requirement of high concurrent read and write in database

Efficient storage and access to massive data

Requirements for high scalability and high availability of database

Storage mode of non-relational database

Key-value mode (Key-value), which stores, deletes and modifies data based on keys

Column storage (Column-oriented) to store related data in a column family

In the form of a document, the database consists of a series of data items, each with a name and a corresponding value

Graphically, entities are vertices, relationships are edges, and data is saved as a graphic

Products of non-relational database

Memcached is an open source, high-performance, caching system with distributed memory objects that stores data in Key-value.

Cache data to reduce database pressure and speed up access

Accelerate dynamic Web application

The contents of the cache are saved in memory

Run in memory, equivalent to a cache, web cache database

Redis also stores data in an one-Key-value way, and the data is also stored in memory, but the data is regularly written to disk.

Compared with Memcached, it has the following characteristics

Support for memory caching

Support for persistence

More data types

Support for clustering, distributed

Support queues

Introduction to Mysql database

Mysql is a popular open source relational database.

Oracle's products

Abide by the GPL agreement, can be used and modified free of charge

Characteristics

Excellent performance and stable service

Open source, no version restriction, low cost

Multi-thread, multi-user

Based on CMARS client or server architecture

Safe and reliable

These are the basic concepts of the database, and the next chapter is the operation command of the database. Thank you for watching.

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