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1、 MySQL introduction

2022-06-26 11:30:00 【Wayne830】

Indexes

1、 Database introduction
2、SQL brief introduction
3、 Relational algebra
4、 Use phpstudy Study MySQL

1、 Database introduction

▲ Definition : database (Database, abbreviation DB) It's organized according to the data structure , Warehouse for storing and managing data .
▲ Characteristics and functions : On data Persistence The preservation of the ; Convenient data storage and query , Fast , Security , convenient ; Can handle concurrent access ; More secure rights management access mechanism .
▲ Definition of relational database and non relational database and common corresponding products
Relational database : use relational model To organize the storage of data , In the form of rows and columns ( surface ) Store data and record the relationship between data , You can maintain the relationship between data by establishing associations between tables . Its common products are :MySQL(MariaDB、Percona Server)、PostgreSQL、Oracle、SQL Server、Access、Sybase etc. .
for example : Student information -> Student list Class information -> Class table
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Non relational database : use Key value pair To store data , Only complete the recording of data , Relationships between data are not recorded . In a non relational database , Solve some big data application problems based on specific storage structure .NoSQL(Not Only SQL) To refer to non relational databases .
① Retrieval Oriented columnar storage (Column-Oriented) Non relational database :HaBase(Hadoop Subsystem )、BigTable(Google company ) etc.
② Cache storage for high concurrency (Key-value) Non relational database :Redis、MemcacheDB etc.
③ Documents for massive data access (Document-Oriented) Stored non relational database ：MongoDB、CouchDB etc.
▲ Database terminology
data (Data): A symbolic record of things .
Relationship : A relation corresponds to a table as is often said .
Tuples : A row in the table is a tuple .
attribute : A column in the table is an attribute , Give each attribute a name, that is, the attribute name .
Database management system (DBMS): A layer of data management software between the user and the operating system .
Database system administrator (DBA): Responsible for database creation , Use and maintenance professionals .
Database system (DBS): Database administrator 、 Database management system and the whole unit of database .
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2、SQL brief introduction

▲ Definition : Structured query language (Structed Query Language), For access 、 Inquire about 、 Update data and manage relational database system .
▲ Development :1981 Year by year IBM The company to launch , Once introduced, the syntax based on its introduction has been widely used in databases , Become the general specification of mainstream database . Later by ANSI The organization determines the specification , Compliance in different database products SQL General specifications , But also with SQL There are some differences , Proprietary instructions that form some databases .
▲ classification : from SQL Different database operations completed by instructions , Can be SQL There are four categories :DDL、DML、DQL、DCL
DDL(Data Definition Language): Data definition language , Used to complete the database object ( database 、 Data sheet 、 View 、 Index, etc. ) The creation of 、 Delete 、 modify .
DML(Data Manipulation Language): Data manipulation language , Used to add, delete, and modify data in the data table .
DQL(Data Query Language): Data query language , It is used to query the data in the data table .
DCL(Data Control Language): Data control language , Used to complete control operations such as transaction management .
▲ Basic grammatical principles
①SQL Instruction is not case sensitive .
② Every one of them SQL The instructions are written in ; end
③SQL Keywords in are separated by spaces .
④SQL There is no limit to line breaks in , That is, you can wrap lines where there are spaces .

3、 Relational algebra

Relationship model R( $A_{1},A_{2},...,A_{n}$ ),t∈R Express t yes R A tuple of .t[ $A_{i}$ ] Represents relative attributes in tuples $A_{i}$ Components of .
R by n Eye relations ,S by m Eye relations . $t_{r}∈R,t_{s}∈S$ , Think $t_{r}t_{s}$ Is the connection of tuples ( concatenated ), It is n+m Column tuple .
Image set : Given the relationship R(X,Z),X and Z For attribute group . When t[X]=x when ,x stay R The set of images is $Z_{x}$ ={t[Z]|t∈R,t[X]=x}.

Relational algebra is an abstract query language , Operations on relationships to express queries . The operations of relational algebra are as follows Operators are different Divided into traditional Set operations And specialized Relationship between operation Two types of .
① Traditional set operations
Set operations are binomial operations , contain and 、 Bad 、 hand over 、 Cartesian product operation . Assume two relationships R and S.
and :R∪S={t|t∈R∨t∈S}
hand over :R∩S={t|t∈R∧t∈S}
Bad :R-S={t|t∈R∧t∉S}
Cartesian product :R×S={ $t_{r}t_{s}$ | $t_{r}∈R∧t_{s}∈S$ }
② Special relational operations
Relational operations include choice 、 Projection 、 Connect 、 except operation .
choice : Also known as restriction . $σ_{F}(R)$ ={t|t∈R∧F(t)=‘true’}. among F To choose conditions , Is a logical expression , Basic form XθY,θ Is a comparison operator or a logical operator .
Projection : Relationship R The projection on is from R Select several attribute columns to form a new relationship . $Π_{A}(R)$ ={t[A]|t∈R}, among A by R Property column in .
Connect : Also known as θ Connect , From the Cartesian product of the two relations, the tuples satisfying certain conditions between tree types are selected . $R⋈S_{AθB}$ ={ $t_{r}t_{s}|t_{r}∈R∧t_{s}∈S∧t_{r}[A]θt_{S}[B]$ }.
except : Relationship R(X,Y) and S(Y,Z), among X,Y,Z It's an attribute group .R Medium Y And S Can have different attribute names , But it has to come from the same set of domains .R÷S={ $t_{r}[X]|t_{r}∈R∧Π_{Y}(S)⊆Y_{x}$ }.
▲ Examples of relational algebra :
https://www.bilibili.com/video/BV1JR4y1j78w?spm_id_from=333.999.0.0

4、 Use phpstudy Study MySQL

For reference :https://blog.csdn.net/qq_45735611/article/details/104820410
First step : Official website https://www.xp.cn/ download phpstudy, Select the destination folder for the download , Direct installation , Open after success phpstudy, And start the MySQL5.7.26 and Nginx1.15.11.
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The second step : Click on " Set up ", Get into MySQL Folder .

The third step : Get into bin Folder , Copy path .

Step four : Right click this computer , choice " attribute ", open " Advanced system setup ", Click on " environment variable ", stay " System variables " Of PATH New China , Add the path copied in step 3 to . Click OK in all windows when exiting .
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Step five : stay phpstudy Choose from " database ", Click on " modify root password " Change the password . The default password is root.

Step six :Win+R, Input cmd Call out command window , Input mysql -uroot -p Instructions , Enter the password reset in step 5 , Successfully logged in , Try typing show databases; Command to view an existing database .
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Step seven : stay " Software management " in , install phpMyAdmin.

Step eight : After successful installation , stay " home page " in , open " Database tools ", choice phpMyAdmin, Enter the login interface . User name input root, Password enter the password reset in step 5 , That is, the login is successful .
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