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Is it just that nvarchar supports multibyte characters? If that is the case, is there really any point, other than storage concerns, to using varchars?
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Each character of an nvarchar column requires 2 bytes of storage whereas a varchar column requires 1 byte per character. Potentially, varchar will be quicker but that may well mean that you cannot store the data that you need.
nvarchar stores data as Unicode, so, if you're going to store multilingual data (more than one language) in a data column you need the N variant.
Use nvarchar when the sizes of the column data entries vary considerably. Use nvarchar(max) when the sizes of the column data entries vary considerably, and the string length might exceed 4,000 byte-pairs.
SQL Server NVARCHAR data type is used to store variable-length, Unicode string data. The following shows the syntax of NVARCHAR : NVARCHAR(n) In this syntax, n defines the string length that ranges from 1 to 4,000. If you don't specify the string length, its default value is 1.
An nvarchar column can store any Unicode data. A varchar column is restricted to an 8-bit codepage. Some people think that varchar should be used because it takes up less space. I believe this is not the correct answer. Codepage incompatabilities are a pain, and Unicode is the cure for codepage problems. With cheap disk and memory nowadays, there is really no reason to waste time mucking around with code pages anymore.
All modern operating systems and development platforms use Unicode internally. By using nvarchar rather than varchar, you can avoid doing encoding conversions every time you read from or write to the database. Conversions take time, and are prone to errors. And recovery from conversion errors is a non-trivial problem.
If you are interfacing with an application that uses only ASCII, I would still recommend using Unicode in the database. The OS and database collation algorithms will work better with Unicode. Unicode avoids conversion problems when interfacing with other systems. And you will be preparing for the future. And you can always validate that your data is restricted to 7-bit ASCII for whatever legacy system you're having to maintain, even while enjoying some of the benefits of full Unicode storage.
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varchar: Variable-length, non-Unicode character data. The database collation determines which code page the data is stored using.
nvarchar: Variable-length Unicode character data. Dependent on the database collation for comparisons.
Armed with this knowledge, use whichever one matches your input data (ASCII v. Unicode).
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