All DOC_IDs are unique to meet the foreign key constraints.

所有DOC_ID都是惟一的，以满足外键约束。

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Adding or dropping unique, distinct, or foreign key constraints.

添加或删除惟一、独特或外键约束。

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Primary key, referential integrity, and check constraints.

主键、引用完整性和检查约束。

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Primary key, referential integrity, and check constraints.

主键、引用完整性和检查约束。

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