|Oracle® Database Reference
11g Release 2 (11.2)
|PDF · Mobi · ePub|
|Default value||Derived from
|Range of values||
NLS_SORT specifies the collating sequence for character value comparison in various SQL operators and clauses, for example,
GROUP BY, comparison conditions (
If the value is
BINARY, then comparison is based directly on byte values in the binary encoding of the character values being compared. The ordering depends on the character set of the compared values, which is either the database character set (for
CLOB) or the national character set (for
If the value is a named linguistic sort, then comparison is defined by this sort. A linguistic sort uses various rules to achieve ordering expected by speakers of one or more natural languages. This is usually the same ordering that is used in dictionaries and/or telephone directories in those languages.
The exact operators and query clauses that obey the
NLS_SORT parameter depend on the value of the
NLS_COMP parameter. If an operator or clause does not obey the
NLS_SORT value, as determined by
NLS_COMP, the collation used is
BINARY comparison is faster and uses less resources than any linguistic comparison but for text in a natural language, it does not provide ordering expected by users.
The value of
NLS_SORT affects execution plans of queries. Because a standard index cannot be used as a source of values sorted in a linguistic order, an explicit sort operation must usually be performed instead of an index range scan. A functional index on the
NLSSORT function may be defined to provide values sorted in a linguistic order and reintroduce the index range scan to the execution plan.
Note:The value of the initialization parameter
NLS_SORTis used to initialize the session value of this parameter, which is the actual value referenced by the SQL query processing. This initial value is overriden by a client-side value if the client uses the Oracle JDBC driver or if the client is OCI-based and the
NLS_LANGclient setting (environment variable) is defined. The initialization parameter value is, therefore, usually ignored.