053第471题

NLS_LENGTH_SEMANTICS参数详解

最新推荐文章于 2022-02-23 16:26:01 发布

聆雨落

最新推荐文章于 2022-02-23 16:26:01 发布

阅读量578

点赞数

CC 4.0 BY-SA版权

分类专栏： oracle 文章标签： ocp

本文链接：https://blog.youkuaiyun.com/adeline_pan/article/details/46813937

oracle 专栏收录该内容

41 篇文章

订阅专栏

本文详细介绍了NLS_LENGTH_SEMANTICS参数的作用及其如何影响数据库中CHAR类型字段的长度语义，默认情况下使用BYTE作为长度单位，可通过设置该参数改为字符数。文章还解释了此设置对不同类型的列的影响以及在会话级和实例级的默认行为。

471.Which of the following would be affected by setting NLS_LENGTH_SEMANTICS=CHAR?
A. All objects in the database
B. Tables owned by SYS and SYSTEM
C. Data dictionary tables
D. NCHAR columns
E. CHAR columns
Answer: E

NLS_LENGTH_SEMANTICS

Property	Description
Parameter type	String
Syntax	`NLS_LENGTH_SEMANTICS =` `string` Example: `NLS_LENGTH_SEMANTICS = 'CHAR'`
Default value	`BYTE`
Modifiable	`ALTER SESSION`
Range of values	`BYTE \| CHAR`

The session-level value of NLS_LENGTH_SEMANTICS specifies the default length semantics to use for VARCHAR2 and CHAR table columns, user-defined object attributes, and PL/SQL variables in database objects created in the session. This default may be overridden by the explicit length semantics qualifiers BYTE and CHAR in column, attribute, and variable definitions.

The instance-level value of NLS_LENGTH_SEMANTICS provides a default for the session-level value if NLS_LENGTH_SEMANTICS it is not set explicitly by the database client through the NLS_LENGTH_SEMANTICS client environment variable (does not apply to JDBC Thin clients), or the ALTER SESSION SET NLS_LENGTH_SEMANTICSstatement.

NCHAR, NVARCHAR2, CLOB, and NCLOB columns are always character-based.

Sessions logged in as SYS do not use the NLS_LENGTH_SEMANTICS parameter. They use BYTE length semantics for all created objects unless overridden by the explicit BYTE and CHAR qualifiers in object definitions (SQL DDL statements).