優化我的長mysql查詢

Question

SELECT 
    n.id, 
    n.title, 
    n.text, 
    n.date, 
    IFNULL(ap.name, a.name) AS name, 
    IFNULL(ap.path, a.path) AS path, 
    IFNULL(ap.extension, a.extension) AS extension, 
    IFNULL(ap.width, a.width) AS width, 
    IFNULL(ap.height, a.height) AS height, 
    IFNULL(ap.server, a.server) AS server, 
    s.id AS source_id, 
    s.name AS source_name 
FROM news n 
LEFT JOIN news_attachments na ON n.id = na.news_id AND na.cover = 1 
LEFT JOIN attachments a ON na.attachments_id = a.id 
LEFT JOIN attachments ap ON a.id = ap.parent AND ap.width = 136 
JOIN sources s ON n.sources_id = s.id 
WHERE n.moderate = 1 AND n.delete = 0 
GROUP BY n.id 
ORDER BY n.date DESC 
LIMIT 25 

我有這個SQL查詢。我有一個問題是否好？也許我可以改進它？

在這部分

LEFT JOIN attachments a ON na.attachments_id = a.id 
LEFT JOIN attachments ap ON a.id = ap.parent AND ap.width = 136 

我加載圖像的預覽，然後選擇：

IFNULL(ap.name, a.name) AS name, 
    IFNULL(ap.path, a.path) AS path, 
    IFNULL(ap.extension, a.extension) AS extension, 
    IFNULL(ap.width, a.width) AS width, 
    IFNULL(ap.height, a.height) AS height, 
    IFNULL(ap.server, a.server) AS server 

這意味着，如果有圖像的預覽，然後使用它以其它方式使用原始圖像

說明：

+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+--------------------------+------+---------------------------------+ 
| id | select_type | table | type | possible_keys        | key     | key_len | ref      | rows | Extra       | 
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+--------------------------+------+---------------------------------+ 
| 1 | SIMPLE  | s  | ALL | PRIMARY,id        | NULL     | NULL | NULL      | 4 | Using temporary; Using filesort | 
| 1 | SIMPLE  | n  | ref | fk_news_sources1_idx      | fk_news_sources1_idx | 4  | base.s.id    | 93 | Using where      | 
| 1 | SIMPLE  | na | ref | PRIMARY,fk_news_has_attachments_news1_idx | PRIMARY    | 4  | base.n.id    | 1 |         | 
| 1 | SIMPLE  | a  | eq_ref | PRIMARY,id        | PRIMARY    | 4  | base.na.attachments_id | 1 |         | 
| 1 | SIMPLE  | ap | ALL | NULL          | NULL     | NULL | NULL      | 3720 |         | 
+----+-------------+-------+--------+-------------------------------------------+----------------------+---------+--------------------------+------+---------------------------------+ 

Answer 1

個

假設所有news記錄有sources，嘗試添加一個索引新聞上moderate，delete和date（按順序），然​​後嘗試以下查詢：

SELECT 
    n.id, 
    n.title, 
    n.text, 
    n.date, 
    IFNULL(ap.name, a.name) AS name, 
    IFNULL(ap.path, a.path) AS path, 
    IFNULL(ap.extension, a.extension) AS extension, 
    IFNULL(ap.width, a.width) AS width, 
    IFNULL(ap.height, a.height) AS height, 
    IFNULL(ap.server, a.server) AS server, 
    s.id AS source_id, 
    s.name AS source_name 
FROM (select * 
     from news 
     WHERE moderate = 1 AND delete = 0 
     ORDER BY date DESC 
     LIMIT 25) n 
LEFT JOIN news_attachments na ON n.id = na.news_id AND na.cover = 1 
LEFT JOIN attachments a ON na.attachments_id = a.id 
LEFT JOIN attachments ap ON a.id = ap.parent AND ap.width = 136 
JOIN sources s ON n.sources_id = s.id 
GROUP BY n.id 

Answer 2

確保附件表有一個鍵父母（或可能更好的一個關鍵涵蓋煩惱父母和寬度）。懷疑這是主要問題。

我懷疑新聞表中的中等和刪除列將不會縮小到足以使索引對他們有用。

我還假設有更多的源記錄比新聞記錄，因此MySQL選擇採取消息來源，並加入新聞，而不是其他的方式。