NLS_SORT

Property	Description
Parameter type	String
Syntax	`NLS_SORT = { BINARY \|` `linguistic_definition` `}`
Default value	Derived from `NLS_LANGUAGE`
Modifiable	`ALTER SESSION`
Range of values	`BINARY` or any valid linguistic definition name

NLS_SORT specifies the collating sequence for ORDER BY queries.

If the value is BINARY, then the collating sequence for ORDER BY queries is based on the numeric value of characters (a binary sort that requires less system overhead).
If the value is a named linguistic sort, sorting is based on the order of the defined linguistic sort. Most (but not all) languages supported by the NLS_LANGUAGE parameter also support a linguistic sort with the same name.

Note:
Setting NLS_SORT to anything other than BINARY causes a sort to use a full table scan, regardless of the path chosen by the optimizer. BINARY is the exception because indexes are built according to a binary order of keys. Thus the optimizer can use an index to satisfy the ORDER BY clause when NLS_SORT is set to BINARY. If NLS_SORT is set to any linguistic sort, the optimizer must include a full table scan and a full sort in the execution plan.

You must use the NLS_SORT operator with comparison operations if you want the linguistic sort behavior.