<pre name="code" class="html">1.sql語句,原理使用臨時表法，效率比較低
delete
  FROM `source`
  WHERE is_deleted=0
          AND (student_id,score_id) IN
      (SELECT f.student_id ,
           f.score_id
      FROM
          (SELECT b.`student_id` AS student_id ,
           b.`score_id` AS score_id
          FROM `source` b
          WHERE b.`is_deleted`=0
          GROUP BY  b.student_id,b.score_id
          HAVING count(*) > 1) f )
              AND id NOT IN
      (SELECT g.id
      FROM
          (SELECT min(c.id) AS id
          FROM `source` c
          WHERE c.`is_deleted`=0
          GROUP BY  c.`student_id`,c.`score_id`
          HAVING count(*)>1) g );

2.臨時表法-需要dba協作
1.停服情況下，原表（備份），建一張臨時表，將原表的唯一資料拷貝到臨時表中，刪除源表，更改臨時表表名
2.非停服情況下去重，新建一張臨時表
insert into temp () values (select distinct * from source)
delete from source where 重複資料 in (select * from temp)
insert into source () values(select * from temp)