mysql表中出现重复数据问题

Question

不知道为什么代码没运行一次，sc表就会出现一组重复的数据啊啊w(ﾟДﾟ)w

CREATE TABLE Student
(sno CHAR(3) CONSTRAINT pk_sno PRIMARY KEY,
 sname VARCHAR(20) UNIQUE,
 age INT NOT NULL
 );
 CREATE TABLE course
 (cno CHAR(3) PRIMARY KEY,
 cname VARCHAR(30),
 credit INT CHECK(credit BETWEEN 1 AND 4),
 teacher VARCHAR(10)
 );
 CREATE TABLE sc
 (sno CHAR(3) ,
 cno CHAR(3) ,
 score INT CHECK( score BETWEEN 1 AND 100),
 PRIMARY KEY(sno,cno),
 FOREIGN KEY(sno) REFERENCES student(sno),
 FOREIGN KEY (cno) REFERENCES course(cno)
 );
 INSERT INTO student
 VALUES ('s1','王刚','19'),('s2','李晓','18');
 INSERT INTO course
 VALUES ('c1','c语言','3','李老师'),('c2','java','2','张老师');
 INSERT IGNORE INTO sc(sno,cno,score)
 VALUES ('s1','c1','99'),('s1','c2','93'),('s2','c1','56');
 SELECT * FROM sc;

Answer 1

清理数据：确保表中没有旧的重复数据。可以使用以下语句清理表：

DELETE FROM sc;

重新插入数据：在清理数据后，再次执行插入操作：

INSERT IGNORE INTO sc(sno, cno, score)
VALUES ('s1', 'c1', 99), ('s1', 'c2', 93), ('s2', 'c1', 56);