NLS parameters can be set using the five methods listed. Put the methods in order from highest to
lowest according to Oracles order of precedence:
A. Default setting
B. Client environment variable
C. Explicit ALTER SESSION statement
D. Inside SQL function
E. Server initialization parameter
A. b, d, e, a, c
B. e, a, b, c, d
C. d, c, b, e, a
D. a, b, d, c, e
E. d, c, b, a, e
NLS setting embedded in a SQL function have the highest precedence,followed by explicit ALTER SESSION staements,client environment variables(which execute an implicit ALTER SESSION statement),server-initialization parameters,and finally default setting.
原文：http://www.cnblogs.com/Babylon/p/7833961.html