[解答] (1) 拒绝删除(Restrict) (2) 连锁性删除(Delete Cascade) (3) 将参考到被删除纪录之外来键值设成空值(Set to Null Value) 5. 请建立一纲要名称为salesSchema，并授权给使用者hrSales。
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（4）表有外键关联，truncate table删除表数据为逐行删除，如果外键指定级联删除(delete cascade)，关联的子表也会会被删除所有表数据。如果外键未指定级联(cascde),truncate table逐行删除数据，如果是父行关联子表行数据，将会...
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Configurable delete-cascade 可控的级联删除
ON Delete CASCADE 级联删除 ; 删除时级联删除依赖行 ; 可以在创建表时设置级联删除
Select Delete Cascade 选择删除级联
cascade delete 级联删除
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。
When an ON delete CASCADE rule is active, all records in the child table with matching foreign key values are deleted when a record is deleted from the parent table.
当ON DELETE CASCADE规则被激活时，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被删除。
Note that the tag's cascade attribute is set to none. That's because we don't want to delete products from the catalog when we delete an order.
这里的标签中的cadcade属性设置为none，这是因为我们在删掉一个订单信息时，不想连订单里的产品信息一并删掉。
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