从另一个表中选择值 - 太慢了

Question

I have a huge problem with the loading time for my query. In this case I need values from the column hg_ft_won (table: values) for the home_team_id and away_team_id (table: matches).

It does work as it should. It only takes really long to load. Does anyone have ideas how to improve that by having an alternative query?

$sql = $conn->query("SELECT m.home_team_name, 
       m.away_team_name, 
       m.home_team_id, 
       m.away_team_id, 
       m.starting_time, 
       m.starting_date, 
       m.match_id, 
       m.season_id, 
       m.competition_id, 
       s.season_name, 
       s.country_name, 
       s.competition_name, 

  (SELECT hg_ft_won 
   FROM `values` v 
   WHERE m.home_team_id = v.team_id 
     AND m.season_id = v.season_id ) AS hg_ft_won1, 

  (SELECT hg_ft_won 
   FROM `values` v 
   WHERE m.away_team_id = v.team_id 
     AND m.season_id = v.season_id ) AS hg_ft_won2, 

FROM matches m, 
     seasons s
WHERE m.season_id = s.id 
AND m.starting_date = '2017-02-11'");

values table

matches table

results from webpagetest.org

Answer 1

Never use commas in the FROM clause. Always use proper, explicit JOIN syntax. This is essentially your query:

SELECT . . .
       (SELECT hg_ft_won 
        FROM `values` v 
        WHERE m.home_team_id = v.team_id AND m.season_id = v.season_id
      ) AS hg_ft_won1, 
      (SELECT hg_ft_won 
       FROM `values` v 
       WHERE m.away_team_id = v.team_id AND
             m.season_id = v.season_id
      ) AS hg_ft_won2,
FROM matches m JOIN 
     seasons s
     ON m.season_id = s.id LEFT JOIN
     competition
     ON competition.id = ?.competition_id 
WHERE m.starting_date = '2017-02-11'");

For this query, you want indexes on:

• matches(starting_date, season_id)
• seasons(id) (probably already there)
• competition(id) (probably already there)
• values(team_id, season_id, hg_ft_won)

I don't know where competition_id is. It should be added at the last key to whichever table it belongs to.

Answer 2

Have a try on this query. Create the required index wherever possible.

SELECT m.home_team_name, 
        m.away_team_name, 
        m.home_team_id, 
        m.away_team_id, 
        m.starting_time, 
        m.starting_date, 
        m.match_id, 
        m.season_id, 
        m.competition_id, 
        s.season_name, 
        s.country_name, 
        s.competition_name, 
        v1.hg_ft_won  AS hg_ft_won1, 
        v2.hg_ft_won  AS hg_ft_won2, 
    FROM matches m 
        INNER JOIN seasons s ON m.season_id = s.id
        LEFT JOIN `values` v1 ON m.home_team_id = v1.team_id  AND m.season_id = v1.season_id
        LEFT JOIN `values` v2 ON m.home_team_id = v2.team_id  AND m.season_id = v2.season_id
    AND m.starting_date = '2017-02-11'