INSERT_UPDATE adds new input data to the table, or updates existing rows with input data that has matching primary key values.

INSERT_UPDATE将新的输入数据添加到表中，或者用具有匹配主键值的输入数据更新现有的行。

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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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ON DELETE CASCADE—When a record is deleted from the parent table, all records in the child table with matching foreign key values are also deleted.

ON DELETE CASCADE — 当一条记录从父表中删除时，子表中的所有记录以及匹配的外键值都全部被删除。

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