刪除冗餘記錄

Question

我有一個表：

+------------+------------------------------------------------------+------+-----+---------+-------+ 
| Field  | Type             | Null | Key | Default | Extra | 
+------------+------------------------------------------------------+------+-----+---------+-------+ 
| person_id1 | int(10)            | NO | MUL | 0  |  | 
| person_id2 | int(10)            | NO | MUL | 0  |  | 
| priority | smallint(5)           | NO |  | 0  |  | 
| link_type | enum('member_of_band','legal_name','performs_as','') | NO |  |   |  | 
+------------+------------------------------------------------------+------+-----+---------+-------+ 

有此表上沒有主鍵，但也有person_id1指標，並在person_id2。

的問題是 - 我們有不一致的數據，例如，這個查詢：

SELECT 
    COUNT(*) as c, person_id1, person_id2 
FROM person_person 
WHERE link_type = "member_of_band" 
GROUP BY person_id1, person_id2 
HAVING c > 1 
LIMIT 10; 

返回：

+---+------------+------------+ 
| c | person_id1 | person_id2 | 
+---+------------+------------+ 
| 2 | 50674235 | 51048792 | 
| 3 | 50674245 | 50715733 | 
| 2 | 50674283 | 50712621 | 
| 2 | 50674322 | 50714244 | 
| 2 | 50674378 | 51048804 | 
| 2 | 50674438 | 51048812 | 
| 4 | 50674442 | 50715733 | 
| 2 | 50674449 | 50716913 | 
| 2 | 50674455 | 51048803 | 
| 3 | 50674469 | 50715733 | 
+---+------------+------------+ 

有沒有辦法去除所有多餘的記錄，並留下那些確定？

所有我想出是：

DELETE person_person FROM person_person 
WHERE (person_id1, person_id2) IN (

    SELECT 
     person_id1, person_id2 
    FROM person_person 
    WHERE link_type = "member_of_band" 
    GROUP BY person_id1, person_id2 
    HAVING COUNT(*) > 1 
    LIMIT 100 

) AND link_type = "member_of_band"; 

但是，這將與雙打刪除所有記錄，我需要刪除只是增加一倍。

mysql> select * from person_person where person_id1 = 50674245 and person_id2 = 50715733; 
+------------+------------+----------+----------------+ 
| person_id1 | person_id2 | priority | link_type  | 
+------------+------------+----------+----------------+ 
| 50674245 | 50715733 |  0 | member_of_band | 
| 50674245 | 50715733 |  0 | member_of_band | 
| 50674245 | 50715733 |  0 | member_of_band | 
+------------+------------+----------+----------------+ 

Answer 1

ALTER IGNORE TABLE person_person ADD UNIQUE INDEX (person_id1, person_id2, link_type);