如何在左连接中使用子查询时优化查询

Question

表格： 请在此处查看以查看表格。 How to query counting specific wins of team and find the winner of the series

问题：

• 如何让更多的查询优化？
• 如何减少查询冗余？
• 如何使此查询更快？

摘要

正如你可以在这个查询例子这一部分是多次使用看看。

WHERE leagueid = 2096 
AND start_time >= 1415938900 
AND ((matches.radiant_team_id= 1848158 AND matches.dire_team_id= 15) 
OR (matches.radiant_team_id= 15 AND matches.dire_team_id= 1848158)) 

---

SELECT matches.radiant_team_id, 
     matches.dire_team_id, 
     matches.radiant_name, 
     matches.dire_name, 
     TA.Count AS teamA, 
     TB.Count AS teamB, 
     TA.Count + TB.Count AS total_matches, 
     SUM(TA.wins), 
     SUM(TB.wins), 
     (CASE 
      WHEN series_type = 0 THEN 1 
      WHEN series_type = 1 THEN 2 
      WHEN series_type = 2 THEN 3 
     END) AS wins_goal 
FROM matches 
LEFT JOIN 
    (SELECT radiant_team_id, 
      COUNT(id) AS COUNT, 
      CASE 
       WHEN matches.radiant_team_id = radiant_team_id && radiant_win = 1 THEN 1 
      END AS wins 
    FROM matches 
    WHERE leagueid = 2096 
    AND start_time >= 1415938900 
    AND ((matches.radiant_team_id= 1848158 
      AND matches.dire_team_id= 15) 
      OR (matches.radiant_team_id= 15 
       AND matches.dire_team_id= 1848158)) 
    GROUP BY radiant_team_id) AS TA ON TA.radiant_team_id = matches.radiant_team_id 
LEFT JOIN 
    (SELECT dire_team_id, 
      COUNT(id) AS COUNT, 
      CASE 
       WHEN matches.dire_team_id = dire_team_id && radiant_win = 0 THEN 1 
      END AS wins 
    FROM matches 
    WHERE leagueid = 2096 
    AND start_time >= 1415938900 
    AND ((matches.radiant_team_id= 1848158 
      AND matches.dire_team_id= 15) 
      OR (matches.radiant_team_id= 15 
       AND matches.dire_team_id= 1848158)) 
    GROUP BY dire_team_id) AS TB ON TB.dire_team_id = matches.dire_team_id 
WHERE leagueid = 2096 
    AND start_time >= 1415938900 
    AND ((matches.radiant_team_id= 1848158 
     AND matches.dire_team_id= 15) 
     OR (matches.radiant_team_id= 15 
      AND matches.dire_team_id= 1848158)) 
GROUP BY series_id 

计划匹配

ID| leagueid| team_a_id| team_b_id| starttime 
1|  2096| 1848158|  15| 1415938900 

Answer 1

我相信这可以在没有子查询的情况下完成。

我提出了以下的匹配表

，并用于下面的查询分组的结果，每系列

SELECT 
     matches.leagueid, 
     matches.series_id, 
     matches.series_type, 
     COUNT(id) as matches, 
     IF(radiant_team_id=1848158,radiant_name, dire_name) AS teamA, 
     IF(radiant_team_id=1848158,dire_name, radiant_name) AS teamB, 
     SUM(CASE 
      WHEN radiant_team_id=1848158 AND radiant_win=1 THEN 1 
      WHEN dire_team_id=1848158 AND radiant_win=0 THEN 1 
      ELSE 0 END) AS teamAwin, 
     SUM(CASE 
      WHEN radiant_team_id=15 AND radiant_win=1 THEN 1 
      WHEN dire_team_id=15 AND radiant_win=0 THEN 1 
      ELSE 0 END) AS teamBwin 

FROM `matches` 
WHERE leagueid = 2096 
    AND start_time >= 1415938900 
AND dire_team_id IN (15, 1848158) 
AND radiant_team_id IN (15, 1848158) 
group by leagueid,series_id,series_type,teamA,teamB 

一个线，其产生以下结果

请注意，将一个系列的结果进行分组时，并不存在辐射团队或可怕团队等。在同一系列赛中，角色和角色可能会被切换多次，所以我只将队名称为teamA和teamB。

现在，看看你之前的问题，我发现你需要根据系列类型和每支球队的胜利来确定系列赛冠军。这将需要包装以前的查询并将其用作子查询，如

SELECT matchresults.*, 
     CASE series_type 
     WHEN 0 then IF(teamAwin>=1, teamA,teamB) 
     WHEN 1 then IF(teamAwin>=2, teamA,teamB) 
     ELSE IF(teamAwin>=3, teamA,teamB) 
     END as winner 

from (THE_MAIN_QUERY) as matchresults 

Answer 2

可能有更有效的方式得到你想要的结果。但是，为了使这个查询更有效率，您可以添加索引。这是多次where条款：

WHERE leagueid = 2096 AND 
     start_time >= 1415938900 AND 
     ((matches.radiant_team_id= 1848158 AND matches.dire_team_id= 15) OR 
     (matches.radiant_team_id= 15 AND matches.dire_team_id= 1848158)) 

条件与or是很难优化。以下指数将有所帮助：matches(leagueid, start_time)。覆盖指数（至少为where条件）为matches(leagueid, start_time, radiant_team_id, dire_team_id)。我会从后面的索引开始，看看它是否能够提高性能，足以满足您的需求。