[ONDELETE[CASCADE|SETNULL] 参照完整性是通过使用如下保留字:FOREIGN KEY 定义那些列为外码; REFERENCES 指明外键对应于哪个表的主键;ON DELETE CASCADE 指明删除被参照关系的元组时,同时删除参照关系中的元组;SETNULL表示置为空值方式。本试题中,部门关系的主键为部门号,职工关系的主键为职工号。其中,部门关系的主键...
FOREIGN KEY (column1, column2,... column_n) REFERENCES parent_table (column1, column2, ... column_n) ON DELETE CASCADE; 1. 2. 3. 4. 5. 示例: alter table tb_products add constraint fk_products_supplier foreign key(supplier_id) references tb_supplier(supplier_id) on delete cascade; ...
FOREIGN KEY (column1,column2,...column_n) REFERENCES parent_table (column1, column2,... column_n) ON DELETE CASECADE ); 演示样例: create table tb_supplier ( supplier_id number not null, supplier_name varchar2(50) not null, contact_name varchar2(50), CONSTRAINT pk_supplier PRIMARY KEY...
在需要实现级联删除的情况下,使用 FOREIGN KEY的ON DELETE CASCADE选项非常方便,但在同一张表中,如果有两个外键引用外表数据,那么最多只能将一个外键设为 ON DELETE CASCADE,其他的引用约束需要使用触发器实现级联删除。 1--建立单词表2IF EXISTS (SELECT * FROM sysobjects WHERE name='Word')3DROP TABLE Word4C...
ALTER TABLE 表名 ADD CONSTRAINT 外键名 FOREIGN KEY(外键字段名) REFERENCES 外表表名(主键字段名) [ON DELETE {RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT}] [ON UPDATE {RESTRICT | CASCADE | SET NULL | NO ACTION | SET DEFAULT}] ...
The syntax for creating a foreign key with cascade delete in an ALTER TABLE statement in Oracle/PLSQL is: ALTER TABLE table_name ADD CONSTRAINT constraint_name FOREIGN KEY (column1, column2, ... column_n) REFERENCES parent_table (column1, column2, ... column_n) ON DELETE CASCADE; Examp...
Using the DELETE CASCADE option in your foreign key constraint definitions means better performance and less code when removing records from tables that have a parent-child relationship defined.
FOREIGN KEY(`parent_id`) REFERENCES `parents`(`id`) ON DELETE CASCADE ); INSERT INTO `childs` VALUES (1,1,'I''m the child'); Only the parent was deleted, child does still exist (with invalid parent id) When executing the same SQL statements with sqllitebrowser the result is as exp...
foreign key(repo_id) references repo_table(repo_id)) user 表:id 为主键 profile 表: uid 为主键 简单来说,若表 profile 的 uid 列 作为外键(外建名称:user_profile),参考的主表的列(references)为 user 表的 id,且联动删除更新操作(on delete cascade on update cascade),则 user 表中删除 id 为 ...
如果在FOREIGN KEY條件約束的 ON UPDATE 和/或 ON DELETE 子句上指定 CASCADE 選項,SQL Server 會針對UPDATE_RULE和/或DELETE_RULE數據行傳回SQL_CASCADE。 如果在FOREIGN KEY條件約束的ON UPDATE和/或ON DELETE 子句上指定 NO ACTION 選項,SQL Server 會針對UPDATE_RULE和/或DELETE_RULE數據行傳回SQL_NO_ACTION...