从titles表获取按照title进行分组
从titles表获取按照title进行分组，注意对于重复的emp_no进行忽略。
http://www.nowcoder.com/questionTerminal/c59b452f420c47f48d9c86d69efdff20
select title , count() t
from (
select distinct emp_no , title from titles
)
group by title
having t>= 2;
/ distinct不要写错了
更简单些
select title , count(distinct emp_no ) t
from titles
group by title
having t>= 2;
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