SQL> desc user_param
 Name                             Null?    Type
 -------------------------------- -------- ------------
 USERNAME                         NOT NULL VARCHAR2(64)
 PARAMETER_NAME                   NOT NULL VARCHAR2(64)
 SETTING                          NOT NULL VARCHAR2(64)

Also make a primary key across USERNAME and PARAMETER_NAME columns to make sure no duplicates get entered:

SQL> alter table user_param add constraint pk_user_param primary key (username, parameter_name);

Then the trigger becomes:

CREATE OR REPLACE TRIGGER set_cursor_sharing AFTER
LOGON ON DATABASE
DECLARE
  usern VARCHAR2(30);
  username varchar2(30);
  cmmd VARCHAR2(64);
  i integer;
  cursor get_values(usern varchar2) IS
   SELECT * FROM user_param where username=usern;
  type usernt is table of user_param%ROWTYPE;
  user_param_t usernt;
BEGIN
  username:=SYS_CONTEXT('USERENV','SESSION_USER');
   FOR user_param_t in get_values(username)
    LOOP
     IF substr(user_param_t.parameter_name,1,1)!='_'
     THEN
      SELECT
       'ALTER SESSION SET ' 
||user_param_t.parameter_name||'='
     ||user_param_t.setting INTO cmmd FROM dual;
      ELSE
       SELECT
        'ALTER SESSION SET '||chr(34)
||user_param_t.parameter_name||chr(34)||'='
     ||user_param_t.setting INTO cmmd FROM dual;
      END IF;
--      dbms_output.put_line(cmmd);
      EXECUTE IMMEDIATE cmmd;
     END LOOP;
     EXCEPTION
      WHEN OTHERS THEN
      NULL;
--      dbms_output.put_line('err on: '||cmmd);
END;
/
Now we can simply add a row to our user_param table and next time the user logs in they will get the new setting. This new form also allows us to have different settings for different schemas. We may want to make a specific users sort area larger, or smaller, another we may want to set specific hash or other settings. Any settings added must be session alterable.

For example: 

SQL> insert into user_param values
(‘APPLTEST’,’SORT_AREA_SIZE’,’10M’); 

Will reset the user APPLTEST’s sort_area_size to 10m on next login.

The procedure will also handle any undocumented parameters that begin with an underscore, or event settings. 

The above trigger should be modified to include more robust exception handling and is for example purposes only.