mysql查询根据时间戳识别和删除重复项

Question

我想建立一个mysql查询来列出所有列a有一个重复列b从一个表。诀窍是我有行上的时间戳，所以我需要基本上确定哪些是较旧的重复项，所以我可以删除它。任何帮助，将不胜感激。

Answer 1

只是例子 - 该查询返回重复的帖子，现在你只需要执行删除

id| title  | text_desc   | created 
------------------------------------------------------- 
1 | The title | description here |2012-02-21 10:58:58 
2 | The title | description here 1 |2012-02-21 10:58:58 
3 | The title | description here 3 |2012-02-21 10:58:58 

    select bad_rows.* 
    from posts as bad_rows 
     inner join (
     select title, MIN(id) as min_id 
      from posts 
      group by title 
      having count(*) > 1 
     ) as good_rows on good_rows.title = bad_rows.title 
      and good_rows.min_id <> bad_rows.id; 

这里是返回行

id| title  | text_desc   | created 
------------------------------------------------------- 
2 | The title | description here 1 |2012-02-21 10:58:58 
3 | The title | description here 3 |2012-02-21 10:58:58 

Answer 2

SELECT FOOCODE,COUNT(*) AS DUPS 
FROM TABLE 
GROUP BY FOOCODE 
HAVING COUNT(FOOCODE)>1; 

上面的查询将返回ü所有的重复。这是你在找什么？

Answer 3

这是你的查询：

DELETE FROM tablename 
WHERE id IN 
(SELECT t1.id 
FROM tablename t1 
JOIN tablename t2 
    ON t2.cola = t1.cola AND t2.colb = t1.colb 
    AND t2.timecol > t1.timecol 
WHERE t1.cola = t1.colb) 

的SELECT语句返回那里cola = colb并有与稍后的日期等匹配的行记录。 DELETE语句删除SELECT返回的所有记录。

如果你正在寻找去除重复cola，那么这是查询：

DELETE FROM tablename 
WHERE id IN 
(SELECT t1.id 
FROM tablename t1 
JOIN tablename t2 
    ON t2.cola = t1.cola 
    AND t2.timecol > t1.timecol)