NLS_COMP

Parameter type	String
Syntax	NLS_COMP = {BINARY | ANSI}
Default value	BINARY
Parameter class	Dynamic: ALTER SESSION

Normally, comparisons in the WHERE clause and in PL/SQL blocks is binary unless you specify the NLSSORT function. By setting NLS_COMP to ANSI, you indicate that comparisons in the WHERE clause and in PL/SQL blocks should use the linguistic sort specified in the NLS_SORT parameter. You must also define an index on the column for which you want linguistic sorts.