相关疑难解决方法(0)

为什么没有一个TRUNCATE上mygroup工作？即使ON DELETE CASCADE SET我得到了:

错误1701(42000):无法截断外键约束中引用的表(mytest.instance,CONSTRAINT instance_ibfk_1FOREIGN KEY(GroupID)REFERENCES mytest.mygroup(ID))

drop database mytest;
create database mytest;
use mytest;

CREATE TABLE mygroup (
   ID    INT NOT NULL AUTO_INCREMENT PRIMARY KEY
) ENGINE=InnoDB;

CREATE TABLE instance (
   ID           INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
   GroupID      INT NOT NULL,
   DateTime     DATETIME DEFAULT NULL,

   FOREIGN KEY  (GroupID) REFERENCES mygroup(ID) ON DELETE CASCADE,
   UNIQUE(GroupID)
) ENGINE=InnoDB;