# 方法一：
# select distinct t3.uid,t3.nick_name,t3.achievement from (
# select t2.uid,t2.start_time,t2.score,u2.achievement,u2.nick_name,
# max(t2.start_time) over(partition by t2.uid) as min_date 
# from (
# select t1.uid,t1.start_time,t1.score from 
# (select e1.uid,e1.start_time,e1.score from exam_record as e1 ) t1 
# union 
# select e2.uid,e2.submit_time as start_time,e2.score from practice_record as e2 
# ) t2 left join user_info as u2 on t2.uid=u2.uid 
# where t2.uid in 
# (select u1.uid from user_info as u1 
# where LEFT(u1.nick_name,2)='牛客' and RIGHT(u1.nick_name,1)='号' 
# and (u1.achievement between 1200 and 2500) )) t3 
# where year(min_date)=2021 and month(min_date)=9 


# 方法二：
select t2.uid,u2.nick_name,u2.achievement
from (
select t1.uid,t1.start_time,t1.score from 
(select e1.uid,e1.start_time,e1.score from exam_record as e1 ) t1 
union 
select e2.uid,e2.submit_time as start_time,e2.score from practice_record as e2 
) t2 left join user_info as u2 on t2.uid=u2.uid 
where t2.uid in 
(select u1.uid from user_info as u1 
where LEFT(u1.nick_name,2)='牛客' and RIGHT(u1.nick_name,1)='号' 
and (u1.achievement between 1200 and 2500) ) 
group by t2.uid,u2.nick_name,u2.achievement 
having  year(max(t2.start_time))=2021 and 
month(max(t2.start_time))=9