如何提高SQL查詢多個連接表的性能

Question

我如何提高性能這個查詢，同時還獲得所需的所有信息..

SELECT 
    tr.id, tr.request_status, tr.note, tr.created_date, 
    c.name AS customer_name, c.mobile_phONe, 
    u.full_name AS created_by_name, tt.name AS ticket_type_name 
FROM 
    ticket_request tr 
LEFT JOIN 
    ticket_type tt ON tt.id = tr.ticket_type_id 
LEFT JOIN 
    users u ON u.id = tr.created_by 
LEFT JOIN 
    customer c ON c.id = tr.customer_id 
WHERE 
    tr.is_deleted != 1 
    AND tr.user_id IN (SELECT u.id FROM users u WHERE u.status = '1') 
GROUP BY 
    tr.id 
ORDER BY 
    tr.created_date DESC 
LIMIT 0,20 

目前，該查詢在7-10秒內運行。

• ticket_request表有大約10萬行
• customers表有300K左右行
• users表ticket_type沒有那麼多（約1K行）

Answer 1

下面的加速技術是免除LIMIT第一個，只有在那之後，再做所有的JOINs。

SELECT tr3.id, tr3.request_status, tr3.note, tr3.created_date, 
     c.name AS customer_name, c.mobile_phONe, 
     u2.full_name AS created_by_name, 
     tt.name AS ticket_type_name 
    FROM 
    (
     SELECT tr1.id 
      FROM ticket_request tr1 
      JOIN users u1 ON u1.id = tr1.created_by 
      WHERE u1.status = '1' 
       AND tr1.is_deleted != 1 
      ORDER BY tr1.created_date DESC 
      LIMIT 0,20 
    ) AS tr2 
    JOIN ticket_request AS tr3 ON tr3.id = tr2.id 
    JOIN user AS u2 ON u2.id = tr3.created_by 
    LEFT JOIN ticket_type tt ON tt.id = tr3.ticket_type_id 
    LEFT JOIN customer c ON c.id = tr3.customer_id 
    ORDER BY tr3.created_date 

的JOINs，所述一箇中的 「衍生自」 表TR2，都在觸摸只有20行之後;這是加速的很大一部分。

這可能是一樣好：

SELECT d.id, d.request_status, d.note, d.created_date, 
     c.name AS customer_name, c.mobile_phONe, d.created_by_name, 
     tt.name AS ticket_type_name 
    FROM 
    (
     SELECT tr.id AS tr_id, tr.request_status, tr.note, tr.created_date, 
       tr.ticket_type_id, tr.customer_id 
       u.full_name AS created_by_name 
      FROM ticket_request tr 
      JOIN users u ON u.id = tr.created_by 
      WHERE u.status = '1' 
       AND tr.is_deleted != 1 
      ORDER BY tr.created_date DESC 
      LIMIT 0,20 
    ) AS d 
    LEFT JOIN ticket_type tt ON tt.id = d.ticket_type_id 
    LEFT JOIN customer c ON c.id = d.customer_id 
    ORDER BY d.created_date 

Answer 2

我假設你正在使用MySQL。如果不是，這個答案可以稍微修改以適應另一個數據庫，但這個概念應該保持不變。您ticket_request表之間

ALTER TABLE ticket_type ADD INDEX (id); 
ALTER TABLE users ADD INDEX (id); 
ALTER TABLE customer ADD INDEX (id);  -- important 

要解釋爲什麼指數會有所幫助，考慮第一LEFT JOIN：您可以添加索引，其涉及您的左邊的右邊與ticket_request列加入所有的ID列ticket_type表。如果沒有索引，對於ticket_request中的每條記錄，數據庫將不得不掃描整個ticket_type表以查找與連接條件相匹配的記錄。從性能角度來看，這是昂貴的。但是對於索引，數據庫可以更快地完成此操作，因爲它「知道」匹配記錄的準確位置（或幾乎完全匹配）。

雖然您提到只有customer表非常大，但您仍可以將索引添加到其他表中。未來，他們可能會變得更大。涉及customer的加入很可能是您查詢中的瓶頸。

Answer 3

這裏的優化最大的機會是LIMIT 0,20

1. ​​是沒有意義的，應予刪除。

2. create index ticket_request_ix_is_deleted_created_date on ticket_request (is_deleted,created_date) and change tr.is_deleted != 1 to tr.is_deleted = 0。

   或者

   create index ticket_request_ix_created_date on ticket_request (created_date)

Answer 4

SELECT 
    tr.id, tr.request_status, tr.note, tr.created_date, 
    c.name AS customer_name, c.mobile_phONe, 
    u.full_name AS created_by_name, tt.name AS ticket_type_name 
FROM 
    ticket_request tr 
LEFT JOIN 
    ticket_type tt ON tt.id = tr.ticket_type_id and tr.is_deleted != 1 
LEFT JOIN 
    users u ON u.id = tr.created_by 
JOIN 
    users u1 ON u1.id = tr.user_id and u1.status = '1' 
LEFT JOIN 
    customer c ON c.id = tr.customer_id 
GROUP BY 
    tr.id 
ORDER BY 
    tr.created_date DESC 
LIMIT 0,20 

嘗試這一點，將與更好的性能工作，調整爲按您的要求

Answer 5

比索引其他，在應用層上可以使用的Memcached（如果你使用PHP）喜歡的東西。這也會給你很好的表現。