1 subselect
1 (fullselect)
2+ 
2? 
2.0 UNION
2.0.1! DISTINCT
2.0.1?
2.0.1 ALL
2.0 EXCEPT
2.0.1! DISTINCT
2.0 INTERSECT
2.0.1! DISTINCT
2.1 subselect
2.1 (fullselect)