>>select mt1.* from mytable1 mt1 LEFT join mytable2 mt2 on mt1.fld1 = mt2.fld1 ;
>>	WHERE mt2.fld1 IS NULL
>>

select mt1.* from mytable1 mt1 ;
	WHERE NOT EXIST ( SELECT * FROM mytable2 mt2;
		WHERE mt1.fld1 = mt2.fld1)

*or 
	
select * from mytable1  ;
	WHERE fld1 NOT IN ( SELECT fld1 FROM mytable2)