Shulou(Shulou.com)06/01 Report--

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Database and SQL1. Database database is a collection of data that can be accessed efficiently by saving a large amount of data and processed by computer. The computer system used to manage databases is called database management system (DBMS). Through DBMS, multiple users can safely and easily manipulate large amounts of data. There are many kinds of databases. Relational database is managed by relational database management system (RDBMS). two。 Why is DBMS so important?

The method of managing data through text files or spreadsheet software is very simple, but it also has some disadvantages:

Data cannot be shared by many people

Saving files from computers connected to the network can be read or edited by multiple users online by sharing settings. However, when one user opens the file, other users cannot edit it. if it is an online mall, when a user buys a product, other users cannot buy it.

Unable to provide the format needed to manipulate large amounts of data

If you want to instantly get the desired data from hundreds of thousands or hundreds of kings of data, you must save the data in the appropriate format, but text files and Excel worksheet lights do not provide the corresponding format.

Question: how do you understand it?

The automation of reading and writing requires programming ability.

Data reading and programming automation can be realized through computer programs, but it must be based on the understanding of data structure and certain computer programming technology. Unable to deal with emergencies

When files are mistakenly deleted, hard disk failure, etc., which can not be read, data may be lost, and the data may be easily read or stolen. 3.DBMS species

= = DBMS is mainly classified by the storage format of the data (the type of database). At this stage, there are mainly five types:

Question: how to understand "DBMS is classified mainly through the saved format of the data"?

Hierarchical database (Hierarchical Database,HDB)

One of the oldest databases, which presents the data in a hierarchical (tree-like) way. Hierarchical data used to be the mainstream of databases, but now it is seldom used with the emergence and popularity of relational databases. Relational database (Relational Database,RDB)

Relational database is the most widely used database. Relational database was born in 1969, which has a long history. Like the Excel table, it uses a two-dimensional table of rows and columns to manage data = =. At the same time, it also uses special SQL (Structured Query Language, structured query language) to operate on the data.

A relational database is like an Excel table: commodity number, commodity name, commodity category, sales, unit price, unit price registration date, 0001T-shirt, clothing, 10005002009-09-200002 punch, office supplies, 5003302009-09, 110003 sports T-shirt, 40002800

Object-oriented database (Object Oriented Database,OODB)

One of the programming languages is called object-oriented programming language. The collection of data and operations on data is managed on an object-by-object basis, hence the name. An object-oriented database is a database used to store these objects.

XML Database (XML Database,XMLDB)

In recent years, XML has become more and more popular as a form of data to interact on the Internet. XML database can process a large number of databases in the form of XML at high speed.

Key value Storage system (Key-Value Store,KVS)

This is a database that is simply used to hold the combination of primary key (Key) and value (Value) used by the query. Readers with knowledge of programming languages can think of it as an associative array or Hash. In recent years, as the key-value storage system has been applied to Web services such as Google, which requires a large amount of data for ultra-high-speed query, it has been paid more and more attention.

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