19 - 查询结果的质量和占比

-- round(avg(rating<3)*100,2)=round(avg(if(rating<3,1,0))*100,2) 
select 
    query_name,round(avg(rating/position),2) quality,round(avg(if(rating<3,1,0))*100,2) poor_query_percentage 
from
    Queries
group by
    query_name;