alter table student drop foreign key student_ibfk_1; 重新添加外键且设置级联操作 alter table 表名add foreign key(子表的字段名) references父表名(父表的主键)级联操作 这里的级联操作可以有两个: on update cascade|set null|restrict on delete cascade|set null|restrict #当主表更新的时候子表同步更新,...
MySQL的语句中用来设定外键的参考动作的子句有两大类:on delete和on update。语法是 [CONSTRAINT [symbol]] FOREIGN KEY [index_name] (col_name, ...) REFERENCES tbl_name (col_name,...) [ON DELETE reference_option] [ON UPDATE reference_option] 1. 2. 3. 4. 5. 由字面可以看出,on delete就...
id int primary key auto_increment, class_name char(20) not null, customer_id int unique, #该字段一定要是唯一的 foreign key(customer_id) references customer(id) #外键的字段一定要保证unique on delete cascade on update cascade ); insert into customer(name,qq,phone) values ('李飞机','3181123...
如果在 FOREIGN KEY 约束的 ON UPDATE 和/或 ON DELETE 子句上指定 NO ACTION 选项,则 SQL Server 将返回UPDATE_RULE和/或DELETE_RULE列的SQL_NO_ACTION。当任何 SQLForeignKeys 参数中存在无效值时, SQLForeignKeys 在执行时返回SQL_SUCCESS。 在这些参数中使用无效值时,SQLFetch 将返回SQL_NO_DATA。
mysql> alter table itcast_student add foreign key (class_id) references itcast_class (class_id)on delete set null; on delete set null:表示删除时,将从表外键设置为null (3)接下来我们删除数据,观察级联操作(set null): (4)删除数据,观察级联操作(cascade): ...
Status:Not a BugImpact on me: None Category:MySQL Server: InnoDB storage engineSeverity:S2 (Serious) Version:5.1.41OS:Windows (Win 7) Assigned to:CPU Architecture:Any Tags:foreign key on update cascade self-reference [27 Oct 2010 11:58] Luca Esculapio ...
mysql>alter table `order` drop foreign key order_ibfk_1;//删除foreign key,mysql里面没有修改foreign key的命令QueryOK,2rows affected(0.10sec)Records:2Duplicates:0Warnings:0//删除后在新增mysql>alter table `order`addforeignkey(u_id)referencesuser(id)on delete cascade on update cascade;QueryOK,2ro...
create tabledep(id int primary key auto_increment,dep_namechar(10),dep_commentchar(60));create tableemp(id int primary key auto_increment,namechar(16),genderenum('male','female')notnulldefault'male',dep_id int,foreignkey(dep_id)referencesdep(id)on update cascade ...
时b_foreign_key_name 为外键名,bfk字段和afk字段都必须存在索引 3、外表为约束表,约束着含有外键的被约束表,即 B 含有一个以 A 作为参考表的外键,则 A 为主 B 为从,若关联on delete on update等动作,则 A 变更 B 会被变更,B 怎样变 A 不必跟随变动,且表 A 中必须事先存在 B 要插入的数据外键列...
From what i understand, ON DUPLICATE KEY UPDATE only applies to a single row in a single table. What i'd like to do is if email or name is different for an existing fbUserId, i'd like to update the changed fields. How would i do this? Also, any thoughts...