1. Create many-to-many
1.Student table
create table students ( id int not null primary key auto_increment, name varchar(45) not null )engine=innodb default charset=utf8;
2.Course table
create table courses ( id int not null primary key auto_increment, name varchar(45) not null )engine=innodb default charset=utf8;
3.Intermediate table
create table stu_cour ( id int not null primary key auto_increment course_id int not null, stu_id int not null, constraint cour foreign key(course_id) references courses(id), constraint stu foreign key(stu_id) references students(id) )engine=innodb default charset=utf8;
4. Insert data
insert into students values (0,"小王"); insert into students values (0,"小宋"); insert into students values (0,"小李"); insert into courses values (0,"语文"); insert into courses values (0,"数学"); insert into courses values (0,"英语"); insert into stu_cour values (0,1,1); insert into stu_cour values (0,1,2); insert into stu_cour values (0,1,3); insert into stu_cour values (0,2,1); insert into stu_cour values (0,2,3); insert into stu_cour values (0,3,2); insert into stu_cour values (0,3,3);
5. Query which subjects student 1 chose
SELECT courses.id,courses.name FROM courses INNER JOIN stu_cour ON stu_cour.course_id=courses.id INNER JOIN students ON students.id= 1 and students.id = stu_cour.stu_id;
SELECT students.name FROM students
INNER JOIN stu_cour ON stu_cour.stu_id =students.id
INNER JOIN courses ON courses.id= 2
and stu_cour.course_id = courses.id;
Create user table:
CREATE TABLE users ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, name VARCHAR(50) NOT NULL )ENGINE=InnoDB DEFAULT CHARSET=utf8;
User information table:
CREATE TABLE users_info ( id INT NOT NULL PRIMARY KEY AUTO_INCREMENT, age int NOT NULL, phone varchar(11) NOT NULL, user_id int not null, constraint user_info foreign key(user_id) references users(id) )ENGINE=InnoDB DEFAULT CHARSET=utf8;2. Insert data
insert into users values (0,"小王");
insert into users values (0,"小宋");
insert into users_info values (0,12,'13812345678',1);
insert into users_info values (0,14,'13812345679',2);
Query all the information of the person:
select * from users inner join users_info on users_info.user_id =users.id;
The above is the detailed content of How to create many-to-many and one-to-one relationships in MySQL. For more information, please follow other related articles on the PHP Chinese website!

MySQLstringtypesimpactstorageandperformanceasfollows:1)CHARisfixed-length,alwaysusingthesamestoragespace,whichcanbefasterbutlessspace-efficient.2)VARCHARisvariable-length,morespace-efficientbutpotentiallyslower.3)TEXTisforlargetext,storedoutsiderows,

MySQLstringtypesincludeVARCHAR,TEXT,CHAR,ENUM,andSET.1)VARCHARisversatileforvariable-lengthstringsuptoaspecifiedlimit.2)TEXTisidealforlargetextstoragewithoutadefinedlength.3)CHARisfixed-length,suitableforconsistentdatalikecodes.4)ENUMenforcesdatainte

MySQLoffersvariousstringdatatypes:1)CHARforfixed-lengthstrings,2)VARCHARforvariable-lengthtext,3)BINARYandVARBINARYforbinarydata,4)BLOBandTEXTforlargedata,and5)ENUMandSETforcontrolledinput.Eachtypehasspecificusesandperformancecharacteristics,sochoose

TograntpermissionstonewMySQLusers,followthesesteps:1)AccessMySQLasauserwithsufficientprivileges,2)CreateanewuserwiththeCREATEUSERcommand,3)UsetheGRANTcommandtospecifypermissionslikeSELECT,INSERT,UPDATE,orALLPRIVILEGESonspecificdatabasesortables,and4)

ToaddusersinMySQLeffectivelyandsecurely,followthesesteps:1)UsetheCREATEUSERstatementtoaddanewuser,specifyingthehostandastrongpassword.2)GrantnecessaryprivilegesusingtheGRANTstatement,adheringtotheprincipleofleastprivilege.3)Implementsecuritymeasuresl

ToaddanewuserwithcomplexpermissionsinMySQL,followthesesteps:1)CreatetheuserwithCREATEUSER'newuser'@'localhost'IDENTIFIEDBY'password';.2)Grantreadaccesstoalltablesin'mydatabase'withGRANTSELECTONmydatabase.TO'newuser'@'localhost';.3)Grantwriteaccessto'

The string data types in MySQL include CHAR, VARCHAR, BINARY, VARBINARY, BLOB, and TEXT. The collations determine the comparison and sorting of strings. 1.CHAR is suitable for fixed-length strings, VARCHAR is suitable for variable-length strings. 2.BINARY and VARBINARY are used for binary data, and BLOB and TEXT are used for large object data. 3. Sorting rules such as utf8mb4_unicode_ci ignores upper and lower case and is suitable for user names; utf8mb4_bin is case sensitive and is suitable for fields that require precise comparison.

The best MySQLVARCHAR column length selection should be based on data analysis, consider future growth, evaluate performance impacts, and character set requirements. 1) Analyze the data to determine typical lengths; 2) Reserve future expansion space; 3) Pay attention to the impact of large lengths on performance; 4) Consider the impact of character sets on storage. Through these steps, the efficiency and scalability of the database can be optimized.


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

SublimeText3 Chinese version
Chinese version, very easy to use

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

MantisBT
Mantis is an easy-to-deploy web-based defect tracking tool designed to aid in product defect tracking. It requires PHP, MySQL and a web server. Check out our demo and hosting services.

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Zend Studio 13.0.1
Powerful PHP integrated development environment
