[转载]为什么一些SQL字符串有'N'前缀？

Why do some SQL strings have an 'N' prefix?


From:   http://databases.aspfaq.com/general/why-do-some-sql-strings-have-an-n-prefix.html

You may have seen Transact-SQL code that passes strings around using an N prefix. This denotes that the subsequent string is in Unicode (the N actually stands for National language character set). Which means that you are passing an NCHAR, NVARCHAR or NTEXT value, as opposed to CHAR, VARCHAR or TEXT. See Article #2354 for a comparison of these data types.

insert into TABLE_NAME (COLUMN1,COLUMN2) values(1,N'中国');

Unicode is typically used in database applications which are designed to facilitate code pages which extend beyond the English and Western Europe code pages (Erland Sommarskog, a native of Sweden, refers to this set as "Germanic and Romance languages"), for example Chinese. Unicode is designed so that extended character sets can still "fit" into database columns. What this means is that Unicode character data types are limited to half the space, because each byte actually takes two bytes (Unicode is sometimes referred to as "double-wide"). For more information on Unicode, see Unicode.org. Note that there are many encoding schemes in the Unicode standard, but SQL Server only supports one: UTF-16.

While using Unicode is a design choice you can make in building your own applications, some facilities in SQL server require it. One example is sp_executeSQL. If you try the following: