Rails使用主键列id来完成各种记录保持和引用任务。
Rails USES the primary key column id for various recordkeeping and referencing tasks.
有关数据库如何使用主键约束的详细信息，请查阅数据库文档。
Consult your database documentation for details about how your database works with primary key constraints.
在关系数据库中通常可以使用主键，它由一个自动递增特性或序列生成器生成。
It is common for relational databases to use the concept of primary keys, generated by an auto-increment feature or by a sequence generator.
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