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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This method takes three parameters, the primary key, the action performed on the table (create, update, delete) and a result set.

此方法具有三个参数，主键、对表执行的操作(创建、更新、删除)和结果集。

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Delete all result set columns except those required by the target table.

删除目标表不需要的所有结果集列。

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Users can choose to delete data after a set period of time, or pass it on to specific people.

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Almost all of the machines ran outdated software with critical security vulnerabilities, and 98% contained data that the company or individual who set up the machine for users had intended to delete but could still be extracted from the machine.

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