When ON delete set NULL is active, when a record is deleted from the parent table, all records in the child table with matching foreign key values are set to NULL.

当ON DELETE SET NULL规则被激活时，如果一条记录从父表中删除，子表中的所有记录以及匹配的外键值都被设置为NULL。

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Furthermore, deleted rows are skipped unconditionally on table scan access while deleted keys are not skipped for type-2 index scans unless the registry variable DB2_SKIPDELETED is also set.

而且，虽然在type - 2索引扫描中，被删除的行不会被跳过，但是除非同时设置了注册表变量db2_skipdeleted，否则在表扫描访问中，被删除的行将被无条件跳过。

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