Tài liệu PL/SQL User’s Guide and Reference phần 2

National Character Types
The widely used one-byte ASCII and EBCDIC character sets are adequate to
represent the Roman alphabet, but some Asian languages, such as Japanese, contain
thousands of characters. These languages require two or three bytes to represent
each character. How does Oracle deal with such dissimilar languages?
Oracle provides National Language Support (NLS), which lets you process
single-byte and multi-byte character data and convert between character sets. It also
lets your applications run in different language environments.
With NLS, number and date formats adapt automatically to the language
conventions specified for a user session. Thus, NLS allows users around the world
to interact with Oracle in their native languages.
PL/SQL supports two character sets called the database character set, which is used
for identifiers and source code, and the national character set, which is used for NLS
data. The datatypes NCHAR and NVARCHAR2 store character strings formed from the
national character set.
Note: When converting CHAR or VARCHAR2 data between databases with different
character sets, make sure the data consists of well-formed strings. For more
information, see Oracle8i National Language Support Guide.