如何删除包含其他表的外键的表中的行

Question

假设有一个包含主键的主表,另一个表包含该主表的外键.因此,如果我们删除主表的行,它也将删除子表.

我该如何写这个查询？

Answer 1

从您的问题来看,我认为可以安全地假设您已启用CASCADING DELETES.
在这种情况下所需要的只是

DELETE FROM MainTable
WHERE PrimaryKey = ???

您的数据库引擎将负责删除相应的引用记录.

Answer 2

首先,作为一次性数据清理练习,删除孤立的行,例如

DELETE 
  FROM ReferencingTable 
 WHERE NOT EXISTS (
                   SELECT * 
                     FROM MainTable AS T1
                    WHERE T1.pk_col_1 = ReferencingTable.pk_col_1
                  );

其次,作为一次性模式更改练习,将ON DELETE CASCADE引用操作添加到引用表上的外键,例如

ALTER TABLE ReferencingTable DROP 
   CONSTRAINT fk__ReferencingTable__MainTable;

ALTER TABLE ReferencingTable ADD 
   CONSTRAINT fk__ReferencingTable__MainTable 
      FOREIGN KEY (pk_col_1)
      REFERENCES MainTable (pk_col_1)
      ON DELETE CASCADE;

然后,永久更新,引用表中的行将在删除其引用行时自动删除.

Answer 3

您可以使用delete cascade选项更改外键约束,如下所示.这将删除与主表行相关的chind表行.

ALTER TABLE MasterTable
ADD CONSTRAINT fk_xyz 
FOREIGN KEY (xyz) 
REFERENCES ChildTable (xyz) ON DELETE CASCADE 

Answer 4

如果要删除多行并且不想更改表的结构，则可以使用游标。1-您首先需要选择要删除的行（在游标中） 2-然后对于游标中的每一行，您删除引用行，然后自己删除该行。

前任：

--id is primary key of MainTable
    declare @id int
    set @id = 1
    declare theMain cursor for select FK from MainTable where MainID = @id
    declare @fk_Id int
    open theMain
    fetch next from theMain into @fk_Id
    while @@fetch_status=0
    begin
        --fkid is the foreign key 
        --Must delete from Main Table first then child.
        delete from MainTable where fkid = @fk_Id
        delete from ReferencingTable where fkid = @fk_Id
        fetch next from theMain into @fk_Id
    end
    close theMain
    deallocate theMain

希望有用