Oracle National Character Set and database Character Set

Server: (oracle Server Character Set) database character set specified during database creation. It cannot be changed after database creation. When creating a database, you can specify the CHARACTERSET and NATIONALCHARACTERSET ). 1. Character Set: (1) used to store CHAR, VARCHAR2, CLOB, LONG, and other types of data (2) used

Server: (oracle Server Character Set) database character set specified during database creation. It cannot be changed after database creation. When creating a database, you can specify the character set and national character set ). 1. Character Set: (1) used to store CHAR, VARCHAR2, CLOB, LONG, and other types of data (2) used

Server: (oracle Server Character Set)
The database character set is specified during database creation and cannot be changed after database creation. When creating a database, you can specify the character set and national character set ).
1. Character Set:
(1) used to store CHAR, VARCHAR2, CLOB, LONG, and other data types
(2) used to mark table names, column names, PL/SQL variables, etc.
(3) used to store SQL and PL/SQL program units
2. National Character Set:
(1) used to store NCHAR, NVARCHAR2, NCLOB, and other data types
(2) The National Character Set is essentially an additional character set selected for oracle. It is mainly used to enhance the character processing capability of oracle, the NCHAR data type can support the use of fixed-length multi-byte encoding in Asia, while the database character set cannot. The National Character Set is redefined in oracle9i and can only be selected from AF16UTF16 and UTF8 in unicode encoding. The default value is AF16UTF16.
3. query character set parameters:
You can query the following data dictionaries or views to view Character Set settings.
Nls_database_parameters, props $, v $ nls_parameters
In the query results, NLS_CHARACTERSET indicates the character set, and NLS_NCHAR_CHARACTERSET indicates the national character set.
4. Modify the database character set:
As mentioned above, the database character set cannot be changed in principle after it is created. If you need to modify the character set, you usually need to export the DATABASE data, recreate the DATABASE, and then import the DATABASE data for conversion, or use the alter database character set statement to modify the character set, however, there are restrictions on modifying the character set after the database is created. Only when the new character set is the current character set superset can the database character set be modified. For example, UTF8 is a superset of US7ASCII. You can use ALTER to modify the character set of the database.

Client: (NLS_LANG parameter)
The client character set defines the encoding method of client character data. Any character data sent from or to the client is encoded using the character set defined by the client. The client can be seen as a variety of applications that can be directly connected to the database, for example, sqlplus, exp/imp. The client character set is set by setting the NLS_LANG parameter.

Differences in national character sets :( AL16UTF16 and UTF-8)
1. Both AL16UTF16 and UTF8 are applicable to national character sets.
2. AL16UFT16 is a fixed-width double-byte Unicode Character Set; UTF8 is a variable-width, one to three bytes Unicode Character Set
3. european characters are stored in UTF8 by one or two bytes, while in AL16UTF16 by two bytes. In contrast, UTF8 can save space. Asian characters are stored in UTF8 by three bytes, the required space is more than AL16UTF16
4. AL16UTF16 is a fixed width encoding, so the execution speed is faster than UTF8 with variable width.

If you use EXP/IMP for Database Export/Import, you should not only pay attention to the character set compatibility between the two servers, but also take into account the export/import process, character Set compatibility between the server and the client, especially when exporting data.