mysql - 如何删除mysql中唯一的记录？

Question

我有一张这样的 table

rowID | StudentName | rollNo | Class
      |             |        |
1     | ABC         |10      |  5   
2     | ABC         |10      |  5
3     | xyz         |11      |  5
4     | asd         |12      |  5

如何删除类为 5 的所有 unique 记录

这样我就有剩余的 table

rowID | StudentName | rollNo | Class
      |             |        |
1     | ABC         |10      |  5  

Answer 1

我认为这符合你的要求:

select min(id), StudentName, rollNo, Class
from t
where class = 5
group by StudentName, rollNo, Class
having count(*) > 1;

如果您确实想要删除记录，那么您需要使用delete:

delete t
    from t left join
         (select studentname, rollno, class, min(id) as min_id, count(*) as cnt
          from t
          group by studentname, rollno, class
         ) tt
         on t.id = tt.minid and tt.cnt > 1
    where tt.minid is null;