Varchar(max) column not allowed to be a Primary Key in SQL Server.
Varchar（max）列不允许是SQL Server中的主键。
What is the max length of a varchar type that can be made a primary key.
可以作为主键的varchar类型的最大长度是多少。
This might be a bad practice, but came across the situation.
这可能是一种不好的做法，但遇到了这种情况。
3 个解决方案
#1
16
900 bytes is the max length for a primary key, this is a bad idea in my opinion, why don't you use a surrogate key instead?
900字节是主键的最大长度，在我看来这是一个坏主意，为什么不使用代理键呢？
#2
5
This question has already been answered in this thread; the short answer is that an index field cannot exceed 900 bytes. That said, it's generally a bad idea to use a long VARCHAR field as an index for myriad reasons such as efficiency and maintainability.
这个问题已经在这个问题中回答了;简短的回答是索引字段不能超过900个字节。也就是说，使用长VARCHAR字段作为索引通常是一个坏主意，因为有很多原因，如效率和可维护性。
#3
3
The primary key is used in all other indexes to identify rows. Having a potentially multi-megabyte value as a key makes very little sense, hence the limit in general on total bytes in any key.
主键在所有其他索引中用于标识行。具有潜在的多兆字节值作为密钥几乎没有意义，因此通常限制任何密钥中的总字节数。
#1
16
900 bytes is the max length for a primary key, this is a bad idea in my opinion, why don't you use a surrogate key instead?
900字节是主键的最大长度，在我看来这是一个坏主意，为什么不使用代理键呢？
#2
5
This question has already been answered in this thread; the short answer is that an index field cannot exceed 900 bytes. That said, it's generally a bad idea to use a long VARCHAR field as an index for myriad reasons such as efficiency and maintainability.
这个问题已经在这个问题中回答了;简短的回答是索引字段不能超过900个字节。也就是说，使用长VARCHAR字段作为索引通常是一个坏主意，因为有很多原因，如效率和可维护性。
#3
3
The primary key is used in all other indexes to identify rows. Having a potentially multi-megabyte value as a key makes very little sense, hence the limit in general on total bytes in any key.
主键在所有其他索引中用于标识行。具有潜在的多兆字节值作为密钥几乎没有意义，因此通常限制任何密钥中的总字节数。