select target_id,
sum(case when comment_level=1 then 1 else 0 end)*1.0/count(*) as haoping,
sum(case when comment_level=2 then 1 else 0 end)*1.0/count(*) as zhongping,
sum(case when comment_level=3 then 1 else 0 end)*1.0/count(*) as chaping
from 评论表
group by target_id