两个我觉得很赞的用法

#无效写法，这样写不会判断表达式（ischecked=0），会全部列出来
SELECT cardid FROM search_detail 
GROUP BY cardid HAVING COUNT(ischecked=0 )>1;
#正确写法，这样如果不满足表达式（ischecked=0），就会置为空，就不计算在内
SELECT cardid FROM search_detail 
GROUP BY cardid HAVING COUNT(ischecked=0 OR NULL)>1;

#巧妙的把同一个cardid的记录分别标了号，这样相邻两条记录就会有同一个标号，减一下就是时间间隔，而首尾的两条记录各对应一条null，不参与计算。
select A.id,B.id idb,A.cardid,A.sintime,B.sintime sintimeb,TIMESTAMPDIFF(DAY,A.sintime,B.sintime) sub_days  
from(  
    select a.*,(@i := @i + 1) as ord_num from loan_16 a,(select @i := 1) d order by cardid,sintime  
) as A LEFT JOIN (  
    select a.*,(@j := @j + 1) as ord_num from loan_16 a,(select @j := 0) c order by cardid,sintime  
)as B on A.ord_num=B.ord_num and A.cardid=B.cardid;