DB2级联删除命令？ [英] DB2 cascade delete command?

问题描述

在DB2上执行级联删除是否有特殊的语法，还是只能通过使用ON DELETE CASCADE选项来创建可级联表来创建级联表？

Is there a special syntax to execute a cascade delete on DB2 or is it only possible to create "cascadable" tables by defining them with the "ON DELETE CASCADE" option?

我想要实现的是在删除该密钥时，基于相同的外键删除其他表行，但是这已经在已经存在和数据填充的数据库上完成。

What I am trying to achieve is delete other table rows based on a same foreign key when I delete that key, but this is done on an already existing and data-filled database.

推荐答案

正如您所说，您必须创建具有 ON DELETE CASCADE 子句，或使用子选择删除预先删除其他行。

As you stated, you either have to create FKs with an ON DELETE CASCADE clause or to pre-delete the other rows with a subselect-delete.

所以，如果你没有一个 ON DELETE CASCADE 子句你必须做

So, if you don't have an ON DELETE CASCADE clause you have to do

DELETE FROM ORDERS_ITEMS WHERE ORDER_ID in (
    SELECT ORDER_ID FROM ORDERS WHERE STATUS = 'Canceled'
);

DELETE FROM ORDERS_ADDRESS WHERE ORDER_ID in (
    SELECT ORDER_ID FROM ORDERS WHERE STATUS = 'Canceled'
);

DELETE FROM ORDERS WHERE STATUS = 'Canceled';

这很简单，但有点多余，所以你可以使用 WITH 语句。

It is simple, but is somewhat redundant so you may use the WITH statement.

如果选择所需行的请求相当大，而如果您没有至少有一个 RR隔离级别，您可能需要使用 TEMPORARY表 ：

If the request to select the required rows is quite big, and if you don't have at least a RR isolation level, you may have to use a TEMPORARY table :

DECLARE GLOBAL TEMPORARY TABLE TMP_IDS_TO_DELETE (ID BIGINT) NOT LOGGED;

INSERT INTO SESSION.TMP_IDS_TO_DELETE (ID)
    SELECT ORDER_ID FROM ORDERS WHERE STATUS = 'Canceled';

DELETE FROM ORDERS_ITEMS WHERE ORDER_ID in (
   SELECT ID FROM SESSION.TMP_IDS_TO_DELETE
);


DELETE FROM ORDERS_ADDRESS WHERE ORDER_ID in (
    SELECT ID FROM SESSION.TMP_IDS_TO_DELETE
);

DELETE FROM ORDERS WHERE ORDER_ID in (
    SELECT ID FROM SESSION.TMP_IDS_TO_DELETE
);

这样您就可以确定您将删除每个表中的相同行，如果你错过了一个FK错误仍然会启动。默认情况下，临时表将在提交时自动清空。

This way you are sure that you will delete the same rows in each table, and a FK error will still fire up if you miss something. Per default, the temporary table will empty itself on commit.

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