爲什麼我的MySQL查詢與多聯接如此緩慢？

Question

我想在大約30,000行的表（history_details）上運行一個查詢，需要連接幾個表（歷史記錄，房間，室友，屬性，listers，學生和管理員）。

1. 第一次加入歷史表很簡單。
2. 只有滿足條件時才應該添加下3個連接（房間，室友，屬性）。在這種情況下，它正在查看history_details表中的listing_type列的值是什麼，並且如果它是適當的值，則應該將該連接添加到查詢中。

3. 之後的3個連接有幾個條件需要滿足才能包含它們，但在這些條件中可能是任何OR條件。

      SELECT SQL_CALC_FOUND_ROWS 
           history_details.history_id, 
           history_details.listing_type, 
           history_details.listing_id, 
           history_details.date_added, 
           history_details.field, 
           history_details.before_value, 
           history_details.after_value, 
           history_details.edit_group, 
           history_details.email, 
           history_details.name, 
           history_details.correction_message, 
           history_details.photo_filepath, 
           history.history_message, 
           listers.first_name, 
           listers.last_name, 
           students.first_name, 
           students.last_name, 
           admin.first_name, 
           admin.last_name 
          FROM history_details 
          LEFT JOIN history 
           ON history_details.history_id = history.history_id 
          LEFT JOIN rooms 
           ON history_details.listing_type="room" AND rooms.room_id = history_details.listing_id 
          LEFT JOIN roommates 
           ON history_details.listing_type="roommate" 
           AND roommates.roommate_id = history_details.listing_id 
          LEFT JOIN properties 
           ON history_details.listing_type="property" 
           AND properties.property_id = history_details.listing_id 
          LEFT JOIN listers 
           ON (history_details.listing_type="lister" AND listers.lister_id = history_details.listing_id) 
           OR (history_details.listing_type="property" AND listers.lister_id = properties.lister_id) 
           OR (history_details.listing_type="room" AND rooms.lister_type="lister" AND listers.lister_id = rooms.lister_id) 
          LEFT JOIN students 
           ON (history_details.listing_type="student" AND students.student_id = history_details.listing_id) 
           OR (history_details.listing_type="roommate" AND students.student_id = roommates.student_id) 
           OR (history_details.listing_type="room" AND rooms.lister_type="student" AND students.student_id = rooms.lister_id) 
          LEFT JOIN admin 
           ON history_details.listing_type="admin" AND admin.admin_id = history_details.listing_id 
          LIMIT 0,100 
   

它給我正確的結果，但它正在73秒運行。我添加了索引，但我不確定它們是否被使用。這是它顯示了當我運行使用EXPLAIN SELECT SQL_CALC_FOUND_ROWS ....

這是它顯示了當我運行使用EXPLAIN SELECT ....

這是我加入的各種表的索引解釋說明： history_details

PR operties

客房

室友

你能告訴我，如果正在使用我的索引？另外，如何改進查詢，表格結構或索引以提高速度？

編輯： 感謝阿馬丹的有益建議，它現在運行在147ms而不是73秒之前。這是最終的查詢我最終使用：

   SELECT SQL_CALC_FOUND_ROWS 
        history_details.*, 
        listers.first_name AS lister_first_name, 
        listers.last_name AS lister_last_name, 
        NULL AS student_first_name, 
        NULL AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN listers 
        ON listers.lister_id = history_details.listing_id 
       WHERE history_details.listing_type="lister" 

       UNION 

       SELECT history_details.*, 
        NULL AS lister_first_name, 
        NULL AS lister_last_name, 
        students.first_name AS student_first_name, 
        students.last_name AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN students 
        ON students.student_id = history_details.listing_id 
       WHERE history_details.listing_type="student" 

       UNION 

       SELECT history_details.*, 
        listers.first_name AS lister_first_name, 
        listers.last_name AS lister_last_name, 
        NULL AS student_first_name, 
        NULL AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN properties 
        ON properties.property_id = history_details.listing_id 
       LEFT JOIN listers 
        ON listers.lister_id = properties.lister_id 
       WHERE history_details.listing_type="property" 

       UNION 

       SELECT history_details.*, 
        listers.first_name AS lister_first_name, 
        listers.last_name AS lister_last_name, 
        students.first_name AS student_first_name, 
        students.last_name AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN rooms 
        ON rooms.room_id = history_details.listing_id 
       LEFT JOIN listers 
        ON (rooms.lister_type="lister" AND listers.lister_id = rooms.lister_id) 
       LEFT JOIN students 
        ON (rooms.lister_type="student" AND students.student_id = rooms.lister_id) 
       WHERE history_details.listing_type="room" 

       UNION 

       SELECT history_details.*, 
        NULL AS lister_first_name, 
        NULL AS lister_last_name, 
        students.first_name AS student_first_name, 
        students.last_name AS student_last_name, 
        NULL AS admin_first_name, 
        NULL AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN roommates 
        ON roommates.roommate_id = history_details.listing_id 
       LEFT JOIN students 
        ON students.student_id = roommates.student_id 
       WHERE history_details.listing_type="roommate" 

       UNION 

       SELECT history_details.*, 
        NULL AS lister_first_name, 
        NULL AS lister_last_name, 
        NULL AS student_first_name, 
        NULL AS student_last_name, 
        admin.first_name AS admin_first_name, 
        admin.last_name AS admin_last_name 
       FROM history_details 
       LEFT JOIN history 
        ON history_details.history_id = history.history_id 
       LEFT JOIN admin 
        ON admin.admin_id = history_details.listing_id 
       WHERE history_details.listing_type="admin" 
       ORDER BY history_details_id DESC 
       LIMIT 0,100 

Answer 1

其中key是NULL中的行，所以不能用這些表的任何索引。即listers和students未被優化。那是因爲它的索引是不可能的，因爲你使用OR來產生它。做幾個查詢，其中每個history_details.listing_type和UNION他們。是的，它看起來很醜，這是很多重複，但速度會在那裏。

聯盟語法如下：

SELECT ... 
WHERE history_details.listing_type="lister" 
UNION 
SELECT ... 
WHERE history_details.listing_type="property" 
UNION 
SELECT ... 
WHERE history_details.listing_type="room" 
UNION 
SELECT ... 
WHERE history_details.listing_type="admin" 
.... 
... 
ORDER BY whatever 
LIMIT whatever, whatever 

確保每個SELECT具有字段（這樣你纔會有無用加入做就算了，但他們會很快，因爲它們會被索引的數量相等）。 ...基本上是您的整個查詢（SELECT field1, field2... FROM table1 LEFT JOIN table2 ON condition ...），但OR取出lister和student條款。 UNION將組合所有子選擇的行。 ORDER和LIMIT將適用於工會的結果，而不是最後的SELECT。