SQL where 子句中的“N" [英] The 'N' in the where clause of SQL

问题描述

我在某处看到了这个查询 -

I saw this query somewhere -

SELECT *
FROM HR.Employees
WHERE country <> N'JAP';

那个 N" 是什么意思?我不确定这是否仅对 SQL 服务器有效.

What does that "N" mean ? I am not sure if this is valid only for SQL server.

推荐答案

N 代表National Character"，表示字符串的内容是 Unicode.

The N stands for "National Character" and it means that the content of the string is Unicode.

每当您遇到可能包含默认 ASCII 字符集之外的字符的专有名称或其他实体时，您都应该使用 Unicode (nchar/nvarchar).如果您不使用 N 前缀将此类字符串括起来，您将丢失数据.例如:

You should be using Unicode (nchar/nvarchar) whenever you might come across proper names or other entities that can contain characters outside of the default ASCII character set. If you don't surround such strings with the N prefix, you will lose data. For example:

SELECT N'ук ферт хер', 'ук ферт хер';

结果:

-----------        -----------
ук ферт хер        ?? ???? ???

您还应该确保在 WHERE 或其他针对 n(var)char 列的子句中使用 N 前缀.当您不使用 N 前缀时，您可能会因隐式转换而遭受严重的性能问题.

You should also be sure to use the N prefix in your WHERE or other clauses against n(var)char columns. When you don't use the N prefix, you could suffer serious performance issues due to implicit conversion.

这篇关于SQL where 子句中的“N"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！