CREATE DATABASE qinfeng;
 USE qinfeng;
CREATE TABLE IF NOT EXISTS students (
student_id INT PRIMARY KEY AUTO_INCREMENT,
 student_name VARCHAR(50) NOT NULL,`
  student_gender VARCHAR(10)，
   student_gende VARCHAR(20)
);
CREATE TABLE IF NOT EXISTS courses (
 course_id INT PRIMARY KEY AUTO_INCREMENT, 
 course_name VARCHAR(100) NOT NULL，
 course_credits INT,
course_grade VARCHAR(20)
);
CREATE TABLE IF NOT EXISTS enrollments(
 enrollment_id INT PRIMARY KEY AUTO_INCREMENT，
 student_id INT, 
 course_id INT,
  score INT,
FOREIGN KEY (student_ d) REFERENCES students(student_id)，
 FOREIGN KEY (course_id)REFERENCES courses(course_id)
 );
INSERT INTO students(student_name,student_gender,student_grade)
 VALUES ('Alice', 'Female', 'Big Data'),
 ('Bob','Male', 'Big Data'),
 ('Carol','Female','Big Data');
INSERT INTO courses (course_name,course_credits,course_grade)
 VALUES ('Database Systems',4,'Computer'),
 ('web Development',3,'Computer');
INSERT INTO enrollments (student_id,course_id,score)
 VALUES (1,1,80)，
 (2,2,70);
SELECT e.enrollment_id,s.student_name,c.course_name,e.enrollment_id
 FROM enrollments e
 JOIN students s ON e.student_id = s.student_id 
 JOIN courses c ON e.course_id = c.course_id;
UPDATE students
 SET student_name='Amy'
 WHERE student_id = 1;
DELETE FROM enrollments
 WHERE course_id =(SELECT course_id FROM courses WHERE course_name = 'webDevelopment');
DELETE FROM Courses
 WHERE course_name = 'web Development';