CREATE TABLE TABLE1(COLUMN1 VARCHAR(20),COLUMN2 VARCHAR(20),COLUMN3 VARCHAR(20))

INSERT INTO TABLE1 VALUES('A','W','SEAT');
INSERT INTO TABLE1 VALUES('B','S','SEAT1');
INSERT INTO TABLE1 VALUES('C','S','SEAT1');
INSERT INTO TABLE1 VALUES('D','S','SEAT1');
INSERT INTO TABLE1 VALUES('A','W','AFGH');

select DISTINCT CASE WHEN (select 'TRUE' from TABLE1 WHERE NOT EXISTS (select * from TABLE1 WHERE COLUMN2<>'S' OR COLUMN2<>'W'))='TRUE' THEN 'TRUE' ELSE 'FALSE' END FROM TABLE1 ;

------------------------------ Commands Entered ------------------------------
SELECT CASE
       WHEN NOT EXISTS
          ( select * from TABLE1
             WHERE COLUMN2 NOT IN ('S', 'W')
          ) THEN
            'TRUE'
       ELSE 'FALSE'
       END  "Answer is"
  FROM SYSIBM.SYSDUMMY1;
------------------------------------------------------------------------------

Answer is
---------
TRUE     

  1 record(s) selected.