Mysql的优化选择查询与IN（）子句

Question

我有这个疑问： - 在里面

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 

的数字（）实际上是另一个表称为标签的IDS其中与用户输入的搜索关键字匹配。在这个例子中，用户搜索了“class”。

参见这里的解释这个查询的输出： - http://www.test.examvillage.com/Screenshot.png

此查询所花费的时间是0.0536秒

但是，如果值在ttagrels.id_tag（）的数量增加（当用户输入更多的搜索关键字时），执行时间上升到1-5秒左右。例如，如果用户搜索“班级可用于导师和学生每天3次”
执行时间为4.2226秒。此查询的说明查询输出在行下包含2513。

All_Tag_Relations表中共有6,152条记录。是否有进一步的优化可能？

Answer 1

我不知道你的数据库，所以我不能给出明确的答案。

我在查询中发现的鲜明关键字两次SUM（DISTINCT（和COUNT（DISTINCT（

这意味着你的SELECT语句返回与相同id_tag或id_od，这意味着几行你的中间结果在分组之前包含许多行，你必须缩小你的where子句以限制行数。

插入在你的查询中计数（*）并且观察行数如果它更大比预期的要好，这解释了你的问题。