有关NLS_DATE_FORMAT设置

NLS_DATE_FORMAT is used if a date format mask is not specified in application code. The effective NLS_DATE_FORMAT is determined by the following (in order of precedence):

 

1. Session NLS_DATE_FORMAT (via ALTER SESSION command)
2. Client side NLS_DATE_FORMAT (from client environment variables/registry settings)
3. Instance NLS_DATE_FORMAT (from init.ora file)
4. Database NLS_DATE_FORMAT

 

Session NLS_DATE_FORMAT is set to client side NLS_DATE_FORMAT (explicit or implicit) ONLY if NLS_LANG is set. Another words, if NLS_LANG is set, then session NLS_DATE_FORMAT will be taken from the client. If clent NLS_LANG is set and client NLS_DATE_FORMAT is not, session NLS_DATE_FORMAT will default to DD-MON-YY (and that was exactly what you experienced). If NLS_LANG is not specified on the client side, NLS_DATE_FORMAT will be taken from instance NLS_DATE_FORMAT which is NLS_DATE_FORMAT from INIT.ORA. If NLS_DATE_FORMAT is not set in INIT.ORA, session NLS_DATE_FORMAT will default to DD-MON-YY.