mysql 添加外键

/**建表语句**/
CREATE TABLE t_student(id int,crosse_id int,name VARCHAR(50));
CREATE TABLE t_crosse(id int,name VARCHAR(50));


/**创建索引**/
CREATE INDEX crosse_index_id  ON t_crosse (id);


/**插入数据**/
INSERT INTO t_crosse VALUES (1001,'语文');
INSERT INTO t_student VALUES (110,1001,'张三');


/**添加外键，添加外键时必须先创建索引，否则外键创建不成功**/
ALTER TABLE `t_student` ADD CONSTRAINT `t_student_crosse_purview_f1` FOREIGN KEY (`crosse_id`) REFERENCES `t_crosse` (`id`) ON DELETE CASCADE ;


/**删除数据查看级联效果**/
DELETE from t_crosse where id = 1001;