如何筛选fieldid相同情况下时间最新的数据呢，麻烦大神帮忙看一下，谢谢了！

SELECT
    d.id,
    d.itemid,
    d.fieldid,
    d.content,
    d.mainuser,
    date_format(
CASE

    WHEN ISNULL( d.maintime ) || d.maintime = str_to_date( '', '%Y-%m-%d' ) THEN
    '' ELSE d.maintime 
    END,
    '%Y-%m-%d' 
    ) maintime,
    ( SELECT username FROM data_user u WHERE u.id = d.mainuser ) mainname 
FROM
    displan_mark d 
WHERE
itemid = 9
```![图片说明](https://img-ask.csdn.net/upload/202002/04/1580800484_343318.png)
如何筛选fieldid相同情况下时间最新的数据呢，麻烦大神帮忙看一下，谢谢了！

select * from displan_mark d join (select dd.fieldid, max(dd.madntime) from displan_mark dd group by dd.fieledid) as v on d.fieldid=v.fieldid