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Function test - Introduction to MySQL database

2022-06-22 01:47:00 【Xiaowu knock code】

MySQL Is the most popular relational database management system , stay WEB Application aspect MySQL It's the best RDBMS(Relational Database Management System： Relational database management system ) One of the application software .

What is a database ？

database （Database） It's organized according to the data structure 、 Warehouse for storing and managing data .

Each database has one or more different API Used to create , visit , management , Search and copy saved data .

We can also store data in files , But reading and writing data in files is relatively slow .

therefore , Now we use a relational database management system （RDBMS） To store and manage large amounts of data . The so-called relational database , It's a database based on a relational model , With the help of set algebra and other mathematical concepts and methods to deal with the data in the database .

RDBMS Relational database management system (Relational Database Management System) Characteristics ：

1. Data is presented in tabular form

2. Name of each record

3. Each column is the data field corresponding to the record name

4. Many rows and columns make up a form

5. Several forms make up database Insert picture description here

RDBMS The term

Before we start to learn MySQL Before database , Let's get to know RDBMS Some of the terms ：

database : A database is a collection of related tables .

Data sheet : A table is a matrix of data . A table in a database looks like a simple spreadsheet .

Column : A column of ( data elements ) Contains the same type of data , For example, postal code data .

** That's ok ：** a line （= Tuples , Or record ） It's a set of related data , For example, a data subscribed by a user .

** redundancy ：** Store twice as much data , Redundancy reduces performance , But it improves the security of the data .

** Primary key ：** The primary key is unique . A data table can only contain one primary key . You can use the primary key to query data .

** Foreign keys ：** Foreign keys are used to associate two tables .

** Composite key ：** Composite key （ Composite key ） Use multiple columns as an index key , Generally used for Composite Index .

** Indexes ：** Use indexes to quickly access specific information in database tables . An index is a structure that sorts the values of a column or columns in a database table . A catalogue similar to a book .

Referential integrity : Referential integrity requires that nonexistent entities cannot be referenced in a relationship . And entity integrity is the integrity constraint that a relational model must satisfy , The purpose is to ensure data consistency .

MySQL Is a relational database (Relational Database Management System), This so-called " Relational type " It can be understood as " form " The concept of , A relational database consists of one or more tables , A table as shown in the figure : Insert picture description here
Header (header): The name of each column ;

Column (col): A collection of data of the same data type ;

That's ok (row): Each line is used to describe the specific information of a record ;

value (value): Details of the line , Each value must be of the same data type as the column ;

key (key): The value of the key is unique in the current column .

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