参考完整性ON DELETE/UPDATE CASCADE是被引用表（父表）中违反时引用表（子表）的联级

mysql> CREATE DATABASE testFK;
Query OK, 1 row affected (0.02 sec)

mysql> USE testFK;
Database changed

mysql> CREATE TABLE course(cNo int NOT NULL,cName VARCHAR(12),PRIMARY KEY(cNo));
Query OK, 0 rows affected (0.06 sec)

mysql> INSERT INTO course VALUES(1,'zucheng'),(2,'shujuku'),(3,'shuxue');
Query OK, 3 rows affected (0.03 sec)
Records: 3  Duplicates: 0  Warnings: 0


mysql> CREATE TABLE Student(sNo int NOT NULL,cNo INT NOT NULL,sName VARCHAR(12),PRIMARY KE
Y(sNo),FOREIGN KEY(cNo) REFERENCES course(cNO) ON DELETE CASCADE ON UPDATE CASCADE);
Query OK, 0 rows affected (0.08 sec)

mysql> INSERT INTO Student VALUES(1,1,'zucheng'),(2,1,'shujuku'),(3,2,'shuxue');
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM student;
+-----+-----+---------+
| sNo | cNo | sName   |
+-----+-----+---------+
|   1 |   1 | zucheng |
|   2 |   1 | shujuku |
|   3 |   4 | shuxue  |
+-----+-----+---------+
3 rows in set (0.00 sec)


mysql> DELETE * FROM course WHERE cNo=4;


mysql> SELECT * FROM student;
+-----+-----+---------+
| sNo | cNo | sName   |
+-----+-----+---------+
|   1 |   1 | zucheng |
|   2 |   1 | shujuku |
+-----+-----+---------+
2 rows in set (0.00 sec)


mysql> UPDATE course set cNo=3 WHERE cNo=1;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1  Changed: 1  Warnings: 0

mysql> SELECT * FROM student;
+-----+-----+---------+
| sNo | cNo | sName   |
+-----+-----+---------+
|   1 |   3 | zucheng |
|   2 |   3 | shujuku |
+-----+-----+---------+
2 rows in set (0.00 sec)

mysql> UPDATE student SET cNo=4 WHERE sNo=1;
ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails (`tes
tfk/student`, CONSTRAINT `student_ibfk_1` FOREIGN KEY (`cNo`) REFERENCES `course` (`cNo`)
ON DELETE CASCADE ON UPDATE CASCADE)
mysql> UPDATE student SET cNo=4 WHERE sNo=1;