题解 | #大小写混乱时的筛选统计#

第一步，求出类别以及对应的数量

select tag, count(*) ct 
from examination_info e1 join exam_record e2
on e1.exam_id = e2.exam_id
group by tag

第二步，自连接，可以直接使用UPPER函数进行连接

select t2.tag tag_,t2.ct,t3.tag ,t3.ct ct_ 
from t1 t2 join t1 t3
on UPPER(t2.tag) = t3.tag
where t2.tag != t3.tag

第三步，选出需要的字段

select tag_, ct_ from (
select t2.tag tag_,t2.ct,t3.tag ,t3.ct ct_ 
from t1 t2 join t1 t3
on UPPER(t2.tag) = t3.tag
where t2.tag != t3.tag
)t1

总的：

with t1 as(
select tag, count(*) ct 
from examination_info e1 join exam_record e2
on e1.exam_id = e2.exam_id
group by tag
)
select tag_, ct_ from (
select t2.tag tag_,t2.ct,t3.tag ,t3.ct ct_ 
from t1 t2 join t1 t3
on UPPER(t2.tag) = t3.tag
where t2.tag != t3.tag
)t1