select * from tab1 a
full outer join tab2 b
on b.col2 = a.col2
full outer join tab3 c
on c.col3 = b.col3
where a.col1 =’123’ and c.col4=’456’
full outer join tab2 b
on b.col2 = a.col2
full outer join tab3 c
on c.col3 = b.col3
where a.col1 =’123’ and c.col4=’456’
full outer join tab2 b
on b.col2 = a.col2
full outer join tab3 c
on c.col3 = b.col3
where a.col1 =’123’ and c.col4=’456’