mysql查询，用于根据时间戳识别和删除重复项

Question

I am trying to build a mysql query to list all column a's that have a duplicate column b from a single table. The trick is I have a timestamp on the rows so i need to essentially identify which is the older of the duplicates so i can delete it. Any help would be appreciated.

Answer 1

Just example - this query return duplicate posts, now you just need to execute delete

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;

Here is the return rows

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

Here's your query:

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)

The SELECT statement returns records where cola = colb and there are other matching rows with a later date. The DELETE statement deletes all records returned by the SELECT.

If you're looking to remove duplicate cola , then this is the query:

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)

Answer 3

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

The above query will return u all the duplicates.Is this what u are looking for?