MySQL查询基于时间戳的一部分删除重复项

Question

I have a webshop which has gotten some duplicate orders because of paypal sending some payment notifications twice or even 3-4-5 times, with random interval between them, ranging from seconds to minutes.

Example from my orders-table:

ID     productname    buyer    timestamp
1      apples         john     2014-07-01 19:22:20
2      bananas        john     2014-07-01 19:22:20
3      oranges        mary     2014-07-01 19:22:52
4      apples         john     2014-07-01 19:22:53
5      bananas        john     2014-07-01 19:22:53
6      apples         chris    2014-07-01 19:22:54

I want to delete all duplicate rows, and by duplicate i mean that productname, buyer and date of purchase should be equal. (only date, not the time part of the timestamp)

So from the table above, this should be deleted:

4      apples         john     2014-07-01 19:22:53
5      bananas        john     2014-07-01 19:22:53

Because he bought the same things earlier the same day.

How would you go about doing this?

Answer 1

you can do it with EXISTS

DELETE FROM table AS t
WHERE EXISTS(
    SELECT * 
    FROM table 
    WHERE id != t.id 
        AND productname = t.productname 
        AND buyer = t.buyer 
        AND DATE(timestamp) = DATE(t.timestamp))

Answer 2

Here is another similar question . What it really comes down to is making the id a unique key field so that you can't insert duplicates in the first place.