主键表的一个记录，关联到关联表中，存在，没有，或者有一个，或者多个记录。这是最重要的也是最常见的关系。

The primary key table contains only one record that relates to none, one, or many records in the related table. This is the most commonly used type of relationship.

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对于创建外键，则需要另外一个具有主键的表，且该主键具有兼容的数据类型。

For foreign key creation, another table with a primary key with a compatible data type is required.

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除了具有主键以外，表通常还有一些辅键。

As well as having primary keys, tables typically have some secondary keys.

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