mysql多表查詢及其 group by 組內排序

 

//多表查詢：得到最新的數據后再執行多表查詢

SELECT *FROM `students` `st` RIGHT JOIN(
  SELECT * FROM 
　　(
　　　　SELECT * FROM goutong WHERE goutongs='asdf' ORDER BY time DESC
　　) AS gtt GROUP BY gtt.name_id ORDER BY gtt.goutong_time DESC ) gt 
　　ON `gt`.`name_id`=`st`.`id` LIMIT 10

 

//先按時間排序查詢，然后分組(GROUP BY ) 
SELECT * FROM 
　　(
　　　　SELECT * FROM goutong WHERE goutongs='asdf' ORDER BY time DESC　　) AS gtt GROUP BY gtt.name_id ORDER BY gtt.time DESC

 

 

參考：http://blog.csdn.net/shellching/article/details/8292338

有數據表 comments
------------------------------------------------
| id | newsID | comment | theTime |
------------------------------------------------
| 1  |        1      |         aaa    |     11       |
------------------------------------------------
| 2  |        1      |         bbb    |     12       |
------------------------------------------------
| 3  |        2      |         ccc     |     12       |

------------------------------------------------

newsID是新聞ID，每條新聞有多條評論comment，theTime是發表評論的時間

現在想要查看每條新聞的最新一條評論：

select * from comments group by newsID 顯然不行

select * from comments group by newsID order by theTime desc 是組外排序，也不行

下面有兩種方法可以實現：

（1）
selet tt.id,tt.newsID,tt.comment,tt.theTime from(  
select id,newsID,comment,theTime from comments order by theTime desc) as tt group by newsID 

（2）
select id,newsID,comment,theTime from comments as tt group by id,newsID,comment,theTime having
 theTime=(select max(theTime) from comments where newsID=tt.newsID)

補充： 通過最大時間 然后再聯合查詢出其它信息，實現避免分組排序的問題。（多個子查詢實現功能）

 

        'SELECT gt.time,  gt.name_id,  gt.goutong,gt.operator, st.id,st.Stu_name,st.Stu_sex,st.stu_gongsi,st.stu_waishangke,st.Stu_jjcourse,st.Stu_phone,st.Stu_beizhu FROM jingjie_students AS st RIGHT JOIN (SELECT A.* FROM jingjie_goutong A, (SELECT name_id,MAX(goutong_time) goutong_time FROM jingjie_goutong WHERE  operator = '小明' GROUP BY name_id) B WHERE A.name_id = B.name_id AND A.time = B.time  ORDER BY A.time DESC LIMIT 0,10) gt ON st.id = gt.name_id';