); #如果需要定义删除主表记录时,从表记录也会随之删除,需要在建立外键约束后添加on delete cascade或者 #添加on delete set null; #on delete cascade:删除主表记录时,把参照该主表记录的从表记录全部级联删除 #on delete set null:删除主表记录时,把参照该主表记录的从表记录的外键设置
KEY(column_name) REFERENCES Table_name(column_name)[ON DELETE CASCADE] SQL>create table userinfo_1 (id varchar2(10) primary key, Username varchar2(30), Orderid varchar2(20), Constraint fk_orderid_1 foreign key(ordered_new)references orderinfo(oderid)); 1. 2. 3. 4. 5. 6. 7. 3....
To verify the installation of PostgreSQL on your machine, you can execute the following command in the command prompt. psql -V When we specify the foreign key constraint in the referencing table using the “ON DELETE CASCADE” keywords, it indicates that the operation performed on the referenced...
class Book(Base): __tablename__ ="book" id = Column(Integer, primary_key=True, index=True, autoincrement=True) title = Column(String, nullable=False) description = Column(String, nullable=True) # relation r_bookmark = relationship("BookMark", back_populates="r_book", cascade="all,de...
我想临时启用ON DELETE CASCADE到所有的外键,这样我就可以轻松地进行批量删除。然后,我想关闭所有外键上的删除级联。据我所知,这样做的唯一方法是使用Management Studio生成一个完整的数据库创建脚本,执行某种类型的搜索和替换以剥离除外键之外的所有内容,保存该脚本,然后执行一些更多的搜索和替换以添加ON DELETE级联。然...
emp_idINTREFERENCESemployees(emp_id)ONDELETECASCADE, order_dateTIMESTAMPDEFAULTCURRENT_TIMESTAMP, total_amountNUMERIC(10,2)NOTNULL); 在这个示例中: order_id是自增的主键。 emp_id是外键,引用employees表的emp_id列。 order_date的默认值为当前时间。
外键创建时可能会导致性能下降的一个情况是,当它与 ON DELETE CASCADE 操作一起使用时。这种操作的机制是,如果父表中的一行被删除,子表中所有引用该行的记录也会在同一事务中被删除。本来可能预期删除一行,结果却可能导致删除数百、数千乃至更多的子表行。但这种情况只有在一个父行与大量子表行关联时才会出现问题...
CASCADE非保留非保留保留保留 CASCADED保留保留保留 CASE保留保留保留保留 CAST保留保留保留保留 CATALOG非保留保留保留 CATALOG_NAME非保留非保留非保留 CEIL保留 CEILING保留 CHAIN非保留非保留非保留 CHAR非保留(不能是函数或类型)保留保留保留 CHARACTER非保留(不能是函数或类型)保留保留保留 ...
> I had defined the foreign key to cascade on delete, and I imagine that > during the dump the delete occurred on the master table. Perhaps the > keyed table had already been dumped so when it came time to dump the > master table, the referencing row was not there to be dumped. ...
i want to delete from C and cascade any delete to E or F but not if there are records in D what i have done is to have ON DELETE CASCADE on C's primary but force deletes to C through a function that will delete from C only ...