with A as ( select '1' col1 from dual union all select '2' col1 from dual union all select '3' col1 from dual union all select '4' col1 from dual ), B as ( select '3' col1 from dual union all select '4' col1 from dual union all select '5' col1 from dual union all select '6' col1 from dual ) select col1 from A where not exists ( select 'x' from B where B.col1 = A.col1) ;
with A as ( select '1' col1 from dual union all select '2' col1 from dual union all select '3' col1 from dual union all select '4' col1 from dual ), B as ( select '3' col1 from dual union all select '4' col1 from dual union all select '5' col1 from dual union all select '6' col1 from dual ) select A.col1 from A, B where A.col1 = B.col1(+) and B.col1 is null