主外键关联,当删除的是父表数据,参照这些要删除的数据,Oracle有三种处理方式: 1、禁止删除,也是Oracle默认方法。 2、将参照要删除数据的子表对应数据置空。...对于2,需要使用on delete set null建立外键约束。...insert into emp_test values (3,'Linda'...
在PostgreSQL 中,可以通过在创建外键约束时指定 ON DELETE CASCADE 来设置级联删除。例如: sql CREATE TABLE parent ( id SERIAL PRIMARY KEY, name TEXT ); CREATE TABLE child ( id SERIAL PRIMARY KEY, parent_id INTEGER REFERENCES parent(id) ON DELETE CASCADE, value TEXT ); 在上述示例中,child 表中...
A表中字段依赖于B表中对应字段, 如果删除B表中的记录,则会级联删除A表中对应记录 createtabletest(id serialprimarykey, namevarchar(10)); createtabletest01(id serialprimarykey, tidint,constraintfk_test01_tidforeignkey(tid)referencestest(id)ondeletecascade); imos=#insertintotest(name)values('a'),('...
[on delete cascade|set null]; 1. 2. 3. 4. 说明: 外键名,Oracle的标识符,建议采用FK_从表名_主表名的方式命名。 主表执行删除行时,其主键值在从表里存在便阻止删除,如果on delete cascade,连带从表的相关行一起删除;如果on delete set null,把从表相关行的外键字段置为null。 2.5、删除外键 AI检测...
on update cascade: 被引用行更新时,引用行自动更新; on update restrict: 被引用的行禁止更新; on delete cascade: 被引用行删除时,引用行也一起删除; on dellete restrict: 被引用的行禁止删除; 3. 删除外键 alter table orders drop constraint orders_goods_id_fkey; ...
The ON DELETE CASCADE is the action on the foreign key that will automatically delete the rows from the child_table whenever corresponding rows from the parent_table are deleted. Let’s take a look at an example. PostgreSQL DELETE CASCADE example First, create tables departments and employees to...
CREATE TABLE orders ( order_id integer PRIMARY KEY, shipping_address text, ... ); CREATE TABLE order_items ( product_no integer REFERENCES products ON DELETE RESTRICT, # 限制删除 order_id integer REFERENCES orders ON DELETE CASCADE, # 级联删除 quantity integer, PRIMARY KEY (product_no, order...
Foreign keys:"table_name_user_id_fkey"FOREIGN KEY (user_id) REFERENCES"users"(id) ON DELETE CASCADE ON UPDATE CASCADE Check constraints:"table_name_check_user_id"CHECK (user_id IS NOT NULL) 这里列出了表中的所有字段名称、数据类型、约束等信息。你可以根据需要查看这些信息。
1. The DELETE statement removes the author with author_id = 2. 2. The ON DELETE CASCADE automatically deletes all books authored by them, maintaining data integrity. Output of the Books Table After executing the above deletion: Key Considerations ...
( objectid bigserial not null, --唯一编号 keys tsvector not null, --关键字 constraint pk_test_cond_objectid primary key (objectid), constraint fk_test_cond_objectid foreign key(objectid) references test(objectid) on delete cascade ); create index idx_test_cond_keys on test_cond using ...