--交集：A∩B
select A.id 
from A 
join B 
on A.id = B.id

--差集：A-B
select A.id 
from A 
left join B 
on A.id = B.id where B.id = ''

--差集：B-A
select B.id 
from A 
right join B 
on A.id = B.id where A.id = ''


--并集：
select number from system.numbers limit 20
union distinct
select number from system.numbers limit 10

--差集 上减下：
select number from system.numbers limit 20
except
select number from system.numbers limit 10

--交集：
select number from system.numbers limit 20
intersect
select number from system.numbers limit 10