Question

我的mysql表名为products，其结构/内容如下：

id (int), public_id (int), deleted (bool), online (bool)
1         1                0               1
2         1                0               0
3         1                1               0
4         2                0               1
5         2                0               1

我的问题是，如何选择所有当前在线但未删除的产品。在此示例中仅记录5（public_id 2）。相同的public_id表示相同的产品（分组）id越高，信息越新（排序）。并且产品需要不删除（在哪里）。还有一些其他的陈述，在这种情况下是在线领域。

我需要所有方面（分组，排序和位置），但我无法弄清楚如何。

有什么建议吗？

来自Galz的解释查询结果：

id  select_type         table         type   possible_keys  key       key_len  ref    rows  Extra
1   PRIMARY             nomis_houses  ref    online         online    1        const  8086  Using where
2   DEPENDENT SUBQUERY  nomis_houses  index  NULL           house_id  4        NULL   9570  Using filesort

PS。这个查询做了诀窍，但非常非常非常缓慢：

select * from 
 (select * from 
  (select * from products order by id desc) tmp_products_1 
 group by public_id) tmp_products_2 
where deleted = '0' AND online = '1'

Answer 1

基于萨钦的回答和你的评论，也许这会有所帮助：

select * from products where id in 
(
   select max(id) as id from products
   where sum(deleted) = 0
   group by public_id
) 
and online = 1

由Pentium10编辑

可以将查询重写为

SELECT * 
FROM   products p 
       JOIN (SELECT MAX(id) AS id 
             FROM   products 
             HAVING  SUM(deleted) = 0 
             GROUP  BY public_id) d 
         ON d.id = p.id 
WHERE  online = 1

您需要索引：

（ID，在线）
（public_id，删除ID）

Answer 2

select * from products where public_id in 
(
   select public_id from products       
   group by public_id
   having sum(deleted) = 0
) 
and online = 1

尝试这项工作正常。子查询提供所有未删除的public_id，然后运行其他联机过滤器。

Answer 3

这个有效吗，但我不知道它的效率。根据萨钦的回答

select p.* from products p where p.public_id in 
(
   select p2.public_id from products p2
   group by p2.public_id
   having sum(p2.deleted) = 0
) 
and p.online = 1 
and p.id = (select max(p3.id) from products p3 where p3.public_id = p.public_id);

MySQL优化

3 个答案: