sql中计算百分比

SELECT CONCAT(CAST(round(((select count() from query_log WHERE user_id =account and is_black>=1 and DATEDIFF(now(),add_time) = 1) /( select count() from query_log WHERE user_id =account and DATEDIFF(now(),add_time) = 1))*100,2) AS CHAR),’%’) as b