Question

我有桌子

id color      image_id
1   red          2
2   green        2
3   pink         2
4   black        2
5   gray         2
6   orange       2
7   purple       2
8   yellow       2
9   greenish     2
10  white        2

select image_id,count(image_id) from colors group by image_id having count(image_id) > 5

如果count大于5，则删除大于5的数据。例如

6   orange       2
7   purple       2
8   yellow       2
9   greenish     2
10  white        2

应该删除

Answer 1

delete from colors
where id not in 
(select id
from colors 
order by id
limit 5)

Answer 2

您希望为每个图片ID保留前五行。这是一个使用变量的方法：

delete i
    from images i join
         (select i.*,
                 (@rn := if(@id = id, @rn + 1,
                            if(@id := id, 0, 0)
                           )
                 ) as rn
          from images i cross join
               (select @id := 0, @rn := 0) vars
          order by image_id, id
         ) ii
         on ii.id = i.id 
    where ii.rn > 5;

Answer 3

您可以使用子查询，然后根据内部联接删除，例如它只会删除它有连接的记录，而在你的子查询中你只会带回你要删除的记录。

delete a
from colors a
inner join
(
select image_id,count(image_id) from colors group by image_id having count(image_id) > 5
) as b
on a.image_id = b.image_id

Answer 4

以下查询将删除除了具有最低颜色ID的前5种颜色之外的所有图像颜色。

delete from colors where id in (
    select id from (
        select c1.id from colors c1
        join colors c2 on c1.image_id = c2.image_id and c2.id < c1.id
        group by c1.id
        having count(*) >= 5
    ) t1
)

如果image_id计数大于5，请删除吗？

4 个答案: