DROP TABLE child; CREATE TABLE child ( id INT, parent_id INT, INDEX par_ind (parent_id), FOREIGN KEY (parent_id) REFERENCES parent(id) ON UPDATE CASCADE ON DELETE CASCADE ) ENGINE=INNODB; Insert some rows into the child table using the statement shown here: mysql> INSERT INTO child ...
1. 主键 超键 候选键 外键 1)超键(super key) :在关系中能唯一标识元组的属性集称为关系模式的超键 2)候选键(candidate key):不含有多余属性的超键称为候选键 3)主键(primary key):用户选作元组标识的一个候选键程序主键 4)外键(foreign key):如果关系模式R1中的某属性集不是R1的主键,而是另一个关系R...
mysql> create table aaa(id int primary key,name char(10) not null,age int); Query OK, 0 rows affected (0.00 sec) mysql> create table bbb(id int primary key,name char(10),uuid int,constraint waijian foreign key(uuid) references aaa(id)); Query OK, 0 rows affected (0.01 sec) #co...
MySQL checks foreign key constraints immediately; the check is not deferred to transaction commit. According to the SQL standard, the default behavior should be deferred checking. That is, constraints are only checked after the entire SQL statement has been processed. This means that it is not ...
for each row|statement [when 触发条件] 触发动作体 如果省略[when 触发条件]则触发动作体在触发器激活后立即执行 row 行级触发器 statement 语句级触发器 如果是行级触发器,用户可以在过程体中使用new和old引用事件之后的新值和事件之前的旧值,如果时语句级触发器,则不能在触发动作体中使用new或old进行引用 ...
This saves you time and efforts of using multiple DELETE statements or a DELETE JOIN statement. The same as deletion, you can also define a cascade on update action for the customerNumber foreign key to perform the cross-table update without using multiple UPDATE statements or an UPDATE JOIN ...
not only am I saying thatnodeidis a foreign key, I'm also using theon delete cascade_ statement to say that whenever the originalnodeis deleted, all records in this table that link back to theidfield in thenodestable should also be deleted. That's very powerful, isn't it? Without for...
在MySQL Workbench 中,打开修改数据表的对话框,进入 Foreign Keys 标签。 Foreign Key Name:外键名称; Referenced Table:关联的主表 Column: 选择外键字段; Referenced Column: 选择主表的关联字段 外键的约束模式: 1.set null: 闲置模式 主表记录被删除或者更改,从表相关记录的外键置为null; ...
MySQL ServerApplicationClientMySQL ServerApplicationClientalt[Constraint Violation]Insert Employee DataExecute SQL StatementCheck Foreign Key ConstraintConstraint Violation ErrorInsert Data into TableInsertion SuccessfulReturn Success 上述序列图展示了一个插入员工数据的流程。当客户端向应用程序发送插入数据的请求时,应...
FOREIGN KEY: 用于预防破坏表之间连接的动作,也能防止非法数据插入外键列,因为它必须是它指向的那个表中的值之一。 CHECK: 用于控制字段的值范围。 5. MySQL 中的 varchar 和 char 有什么区别? char 是一个定长字段,假如申请了char(10)的空间,那么无论实际存储多少内容.该字段都占用 10 个字符,而 varchar 是...