How to disable foreign key constraint checking in MySQL child tables

Prepare:

Define a teacher table and a student table; reference the teacher table ID in the student table

create table teachers(teacherID int not null auto_increment primary key,teacherName varchar(8));

create table students(studentID int not null auto_increment primary key,teacherID int not null,studentName varchar(8),

constraint fk_students_teacherID foreign key (teacherId) references teachers(teacherId) on delete no action on update cascade);

first step:

Insert a teacher

insert into teachers(teacherName) values('NameA');

Insert a student:

insert into students(studentName,teacherID) values('NameB',100);--You can know that there is no such teacher ID, so the insertion will fail.

But is there any way to insert an unreasonable piece of data? There is still a way

Step 2:

set foreign_key_checks = 0; and that's it.

insert into students(studentName,teacherID) values('NameB',100);

Step 3:

Set back to default value, keep foreign key constraint checking.

set foreign_key_checks = 1;

Summarize:

This essay is very messy. The main point I want to make is that foreign key constraints are useless when set foreign_key_checks = 0;. At this time, you can insert into the child table that violates the foreign key constraint.

Don't use this unless absolutely necessary.

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