如果您使用NVARCHAR只是因为系统存储过程需要它，最常见的情况是莫名其妙的sp_executesql，并且您的动态SQL非常长，那么从性能角度来看，您最好在VARCHAR中进行所有字符串操作(连接、替换等)，然后将最终结果转换为NVARCHAR并将其输入到proc参数中。所以，不要总是使用NVARCHAR!

在过去的几年里，我们所有的项目都使用了NVARCHAR，因为所有这些项目都是多语言的。从外部源导入的数据(例如ASCII文件等)在插入到数据库之前被上转换为Unicode。

我还没有遇到任何与较大索引相关的性能问题，等等。索引确实会使用更多的内存，但是内存很便宜。

无论您是使用存储过程还是动态构造SQL，都要确保所有字符串常量都有N前缀(例如SET @foo = N' hello world.';)，这样常量也是Unicode。这避免了在运行时进行任何字符串类型转换。

YMMV。

由于您的应用程序很小，使用nvarchar与使用varchar相比，基本上没有明显的成本增加，而且如果您需要存储unicode数据，您也省去了潜在的麻烦。

如果您使用NVARCHAR只是因为系统存储过程需要它，最常见的情况是莫名其妙的sp_executesql，并且您的动态SQL非常长，那么从性能角度来看，您最好在VARCHAR中进行所有字符串操作(连接、替换等)，然后将最终结果转换为NVARCHAR并将其输入到proc参数中。所以，不要总是使用NVARCHAR!

Generally speaking; Start out with the most expensive datatype that has the least constraints. Put it in production. If performance starts to be an issue, find out what's actually being stored in those nvarchar columns. Is there any characters in there that wouldn't fit into varchar? If not, switch to varchar. Don't try to pre-optimize before you know where the pain is. My guess is that the choice between nvarchar/varchar is not what's going to slow down your application in the foreseable future. There will be other parts of the application where performance tuning will give you much more bang for the bucks.

I can speak from experience on this, beware of nvarchar. Unless you absolutely require it this data field type destroys performance on larger database. I inherited a database that was hurting in terms of performance and space. We were able to reduce a 30GB database in size by 70%! There were some other modifications made to help with performance but I'm sure the varchar's helped out significantly with that as well. If your database has the potential for growing tables to a million + records stay away from nvarchar at all costs.