MySQL的優化

Question

我有mysql-表稱爲產品具有以下結構/內容：

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 

我的問題是，如何選擇全部，當前在線，不刪除產品。在這個例子中只記錄5（public_id 2）。相同的public_id表示相同的產品（分組）。id越高，信息越新（排序）。並且產品需要而不是已刪除（其中）。還有一些其他地方的聲明，在這種情況下與在線領域。

我需要所有方面（分組，排序和地方），但我不知道如何。

有什麼建議嗎？的

結果從Galz解釋查詢：

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。此查詢的伎倆，但非常，非常，非常緩慢：

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

基於薩欽的答案，你的評論，也許這可以幫助：

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

編輯由Pentium10

查詢可以改寫成

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 

你需要的索引：

• （ID，在線）
• （public_id，刪除，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 

嘗試，如果能正常工作。子查詢會提供所有未被刪除的public_id，然後運行其他聯機的篩選器。

Answer 3

嗯，這工作，但我不知道它的效率。基於薩欽的回答

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);