Basics

CREATE TABLE teachers (  id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, nameTeacher VARCHAR(255) NOT NULL, egn INT(10) NOT NULL UNIQUE, address VARCHAR(255) NOT NULL )
CREATE TABLE subjects ( nameSubject VARCHAR(255) NOT NULL, id INT NOT NULL AUTO_INCREMENT PRIMARY KEY )
CREATE TABLE class ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, nameClass VARCHAR(255) )
CREATE TABLE teachers_subjects ( teachers_id INT NOT NULL, CONSTRAINT FOREIGN KEY (teachers_id) REFERENCES teachers(id), subjects_id INT NOT NULL, CONSTRAINT FOREIGN KEY (subjects_id) REFERENCES subjects(id), PRIMARY KEY (teachers_id, subjects_id) )
CREATE TABLE subjects_class( subjects_id INT NOT NULL, CONSTRAINT FOREIGN KEY (subjects_id) REFERENCES subjects(id), class_id INT NOT NULL, CONSTRAINT FOREIGN KEY (class_id) REFERENCES class(id), PRIMARY KEY (subjects_id, class_id) )

UPDATE teachers
SET nameTeacher = 'Galina Ivanova'
WHERE egn = '7623849210';

DELETE FROM teachers
WHERE id = 1;

DELETE FROM teachers
WHERE id IN(1,3,4);

DELETE FROM teachers
WHERE id>=1 AND id<=25;