SQL Developer

I have confusion about COMMIT command. Is it compulsary to run COMMIT command after DML operation in Sql Developer.

Because i was done with an UPDATE query..

UPDATE TAB1 
SET TBX_TYP='ZX'
WHERE TBX_TYP IN(SELECT TBX_TYP
                                  FROM(SELECT DISTINCT TBX_TYP 
                                               FROM TAB1 ORDER BY 1 )
                                 WHERE ROWNUM=1);

and when i did filtering on columns then i found nothing was updated. Please suggest.