主键与聚集索引的关系
TABLE 可以有主键而没有聚集索引吗?
Can a TABLE have a primary key without a clustered index?
TABLE 是否可以有聚集索引而没有主键?
And can a TABLE have a clustered index without having a primary key?
谁能简单介绍一下主键和聚集索引的关系?
Can anybody briefly tell me the relationship between primary key and clustered index?
推荐答案
主键是一个逻辑概念 - 它是表中行的唯一标识符.因此，它有一堆属性——它不能为空，而且必须是唯一的.当然，由于您可能经常通过唯一标识符搜索记录，因此最好在主键上建立索引.
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 - 它是一个影响记录在磁盘上存储顺序的索引.这使它在访问数据时成为一个非常快的索引，但如果您的主键不是序列号，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，您可以拥有一个没有聚集索引的主键 - 有时，您可能想要(例如，当您的主键是连接表上的外键组合，并且您不想招致写入时的磁盘洗牌开销).
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集索引.
Yes, you can create a clustered index on columns that aren't a primary key.
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