varchar2(n) 和 varchar2(n char) 之间的 Oracle SQL 区别
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Oracle SQL difference between varchar2(n) and varchar2(n char)
提问by Ram
Scripts here at work always declare varchar2 columns as varchar2(n char). I do not see any difference and just curious. Thanks!
工作中的脚本总是将 varchar2 列声明为 varchar2(n char)。我没有看到任何区别，只是好奇。谢谢！
回答by Wayan Wiprayoga
Based on this resource
基于此资源
Oracle9i and above allow Varchar2 columns to be defined as a number of bytes VARCHAR2(50 BYTE) or a number of characters VARCHAR2(50 CHAR), the latter is useful if the database is ever converted to run a double-byte character set(such as Japanese), you won't have to edit the column sizes. The default measure, normally BYTE, is set with nls_length_semantics.
If you create a column as Varchar2 (50) but only store 10 bytes, then Oracle will only save 10 bytes to disc. This does not mean that you should just create Varchar2 (4000) columns 'just in case the space is needed', that is a really bad idea which will reduce the performance and maintainability of your application.
Oracle9i 及更高版本允许将 Varchar2 列定义为字节数 VARCHAR2(50 BYTE) 或字符数 VARCHAR2(50 CHAR)，如果将数据库转换为运行双字节字符集（例如作为日语），您将不必编辑列大小。默认度量，通常是 BYTE，是用 nls_length_semantics 设置的。
如果将列创建为 Varchar2 (50) 但仅存储 10 个字节，则 Oracle 将仅将 10 个字节保存到磁盘。这并不意味着您应该只创建 Varchar2 (4000) 列“以防万一需要空间”，这是一个非常糟糕的主意，它会降低应用程序的性能和可维护性。
回答by jim mcnamara
The syntax is VARCHAR2(n)and VARCHAR2(n BYTE|CHAR)
语法是VARCHAR2(n)和VARCHAR2(n BYTE|CHAR)
The default for (n) and (n BYTE) are usually the same. (n CHAR) may not be equivalent to (n|BYTE) or (n) unless you set NLS_LENGTH_SEMANTICSparameter to what you want, CHAR or BYTE. This setting is for character sets that use multibyte characters. Generally not for UTF8, for example.
(n) 和 (n BYTE) 的默认值通常相同。(n CHAR) 可能不等价于 (n|BYTE) 或 (n) 除非您将NLS_LENGTH_SEMANTICS参数设置为所需的 CHAR 或 BYTE。此设置适用于使用多字节字符的字符集。例如，通常不适用于 UTF8。
DO NOT change it, since there is existing code that works.
不要更改它，因为现有代码有效。
I would guess that (n) == (n CHAR) == (n BYTE) or your system.
我猜 (n) == (n CHAR) == (n BYTE) 或您的系统。
