主键和聚集索引的关系 [英] Relationship of Primary Key and Clustered Index

问题描述

TABLE有没有聚集索引的主键？

Can a TABLE have primary key without Clustered Index?

和一个TABLE有没有主键的聚集索引？

and Can a TABLE have Clustered Index without primary key?

任何人都可以简单地告诉我主键和聚集索引的关系？

Can anybody briefly tell me the relationship of primary key and clustered index?

推荐答案

主键是 logical concept - 它是表中行的唯一标识符。因此，它有一堆属性 - 它可能不为null，它必须是唯一的。当然，因为你很可能通过其唯一的标识符搜索记录很多，所以在主键上有一个索引是很好的。

A primary key is a logical concept - it's the unique identifier for a row in a table. As such, it has a bunch of attributes - it may not be null, and it must be unique. Of course, as you're likely to be searching for records by their unique identifier a lot, it would be good to have an index on the primary key.

聚集索引是一个物理概念 - 它是一个影响记录存储在磁盘上的顺序的索引。这使得它在访问数据时速度非常快，但如果主键不是序列号，它可能会减慢写入速度。

A clustered index is a physical concept - it's an index that affects the order in which records are stored on disk. This makes it a very fast index when accessing data, though it may slow down writes if your primary key is not a sequential number.

是的，您可以使用没有聚集索引的主键 - 有时，您可能想要（例如，当您的主键是外键的组合加入表，并且你不想在写时产生磁盘shuffle开销）。

Yes, you can have a primary key without a clustered index - and sometimes, you may want to (for instance when your primary key is a combination of foreign keys on a joining table, and you don't want to incur the disk shuffle overhead when writing).

是的，您可以在不是主键的列上创建聚簇索引。

Yes, you can create a clustered index on columns that aren't a primary key.

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