Oracle: DBMS_SESSION.SET

dbms_session.set_nls is equivalent to alter session set nls-parameter.

ORA-00922: missing or invalid option

The value of the option being set must be enclosed in apostrophes. The following statement throws ORA-00922: missing or invalid option:

begin
   dbms_session.set_nls('nls_date_format', 'dd.mm.yyyy');
end;
/

However, this works ok:

begin
   dbms_session.set_nls('nls_date_format', '"dd.mm.yyyy"');
end;
/