mysql多表查詢及其 group by 組內排序

標籤：

 

//多表查詢：得到最新的資料後再執行多表查詢

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，然後分組(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

有資料表 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)

mysql多表查詢及其 group by 組內排序