Mysql的優化選擇查詢與IN（）子句

Question

我有這個疑問： - 在裏面

SELECT SUM(DISTINCT(ttagrels.id_tag IN (1816, 2642, 1906, 1398, 
              2436, 2940, 1973, 2791, 1389))) AS 
     key_1_total_matches, 
     IF((od.id_od > 0), COUNT(DISTINCT(od.id_od)), 0)     AS 
     tutor_popularity, 
     td.*, 
     u.* 
FROM tutor_details AS td 
     JOIN users AS u 
     ON u.id_user = td.id_user 
     JOIN all_tag_relations AS ttagrels 
     ON td.id_tutor = ttagrels.id_tutor 
     LEFT JOIN learning_packs AS lp 
     ON ttagrels.id_lp = lp.id_lp 
     LEFT JOIN learning_packs_categories AS lpc 
     ON lpc.id_lp_cat = lp.id_lp_cat 
     LEFT JOIN learning_packs_categories AS lpcp 
     ON lpcp.id_lp_cat = lpc.id_parent 
     LEFT JOIN learning_pack_content AS lpct 
     ON (lp.id_lp = lpct.id_lp) 
     LEFT JOIN webclasses AS wc 
     ON ttagrels.id_wc = wc.id_wc 
     LEFT JOIN learning_packs_categories AS wcc 
     ON wcc.id_lp_cat = wc.id_wp_cat 
     LEFT JOIN learning_packs_categories AS wccp 
     ON wccp.id_lp_cat = wcc.id_parent 
     LEFT JOIN order_details AS od 
     ON td.id_tutor = od.id_author 
     LEFT JOIN orders AS o 
     ON od.id_order = o.id_order 
WHERE (u.country = 'IE' 
      OR u.country IN ('INT')) 
     AND u.status = 1 
     AND CASE 
      WHEN (lp.id_lp > 0) THEN lp.id_status = 1 
             AND lp.published = 1 
             AND lpcp.status = 1 
             AND (lpcp.country_code = 'IE' 
               OR lpcp.country_code IN ('INT') 
              ) 
      ELSE 1 
      END 
     AND CASE 
      WHEN (wc.id_wc > 0) THEN wc.wc_api_status = 1 
             AND wc.id_status = 1 
             AND wc.wc_type = 0 
             AND 
      wc.class_date > '2010-06-16 11:44:40' 
             AND wccp.status = 1 
             AND (wccp.country_code = 'IE' 
               OR wccp.country_code IN ('INT') 
              ) 
      ELSE 1 
      END 
     AND CASE 
      WHEN (od.id_od > 0) THEN od.id_author = td.id_tutor 
             AND o.order_status = 'paid' 
             AND CASE 
      WHEN (od.id_wc > 0) THEN od.can_attend_class = 1 
      ELSE 1 
              END 
      ELSE 1 
      END 
     AND (ttagrels.id_tag IN (1816, 2642, 1906, 1398, 
            2436, 2940, 1973, 2791, 1389)) 
GROUP BY td.id_tutor 
HAVING key_1_total_matches = 1 
ORDER BY tutor_popularity DESC, 
      u.surname ASC, 
      u.name ASC 
LIMIT 0, 20 

的數字（）實際上是另一個表稱爲標籤的IDS其中與用戶輸入的搜索關鍵字匹配。在這個例子中，用戶搜索了「class」。

參見這裏的解釋這個查詢的輸出： - http://www.test.examvillage.com/Screenshot.png

此查詢所花費的時間是0.0536秒

但是，如果值在ttagrels.id_tag（）的數量增加（當用戶輸入更多的搜索關鍵字時），執行時間上升到1-5秒左右。例如，如果用戶搜索「班級可用於導師和學生每天3次」
執行時間爲4.2226秒。此查詢的說明查詢輸出在行下包含2513。

All_Tag_Relations表中共有6,152條記錄。是否有進一步的優化可能？

Answer 1

我不知道你的數據庫，所以我不能給出明確的答案。

我在查詢中發現的鮮明關鍵字兩次SUM（DISTINCT（和COUNT（DISTINCT（

這意味着你的SELECT語句返回與相同id_tag或id_od，這意味着幾行你的中間結果在分組之前包含許多行，你必須縮小你的where子句以限制行數。

插入在你的查詢中計數（*）並且觀察行數如果它更大比預期的要好，這解釋了你的問題。