union 专题

union：对合并结果去重
union all：保留所有合并结果

力扣602：

with tmp1 as 
((select requester_id as id 
from RequestAccepted)
union all
(select accepter_id id 
from RequestAccepted))

select id,count(id) as num
from tmp1
group by id
order by num desc
limit 1

-END