此查询大约需要9秒钟，并返回2条记录。
SELECT
s.description, s.improvement,
s.first_name, s.last_name, s.finding, s.action, s.share,
s.learned, s.timestamp, d.title as department_title,
group_concat(DISTINCT g.title SEPARATOR " | ") as strategic_goals,
group_concat(DISTINCT m.statement SEPARATOR " | ") as mission_references,
group_concat(DISTINCT meas.statement SEPARATOR " | ") as measure_statement,
group_concat(DISTINCT o.statement SEPARATOR " | ") as outcome_statement,
group_concat(DISTINCT i.title SEPARATOR " | ") as ilo_title,
group_concat(DISTINCT cv.title SEPARATOR " | ") as core_value_title,
y1.year as current_year_title, y2.year as previous_year_title,
u.file_name as file_name
FROM summary s
LEFT JOIN year y1 ON s.current_year_id = y1.id
INNER JOIN year y2 ON s.previous_year_id = y2.id
INNER JOIN strategic_goal_entries sge ON s.id = sge.summary_id
INNER JOIN goal g ON sge.goal_id = g.id
INNER JOIN outcome o ON s.id = o.summary_id
LEFT JOIN measure meas ON o.id = meas.outcome_id
INNER JOIN department d ON s.department_id = d.id
LEFT JOIN uploads u ON s.id = u.summary_id
INNER JOIN mission_entries me ON s.id = me.summary_id
LEFT JOIN mission m ON me.mission_id = m.id
LEFT JOIN ilo_entries ie ON s.id = ie.summary_id
LEFT JOIN ilo i ON ie.ilo_id = i.id
INNER JOIN core_value_entries cve ON s.id = cve.summary_id
INNER JOIN core_value cv ON cve.core_value_id = cv.id
INNER JOIN executive_of_department eod ON s.department_id = eod.department_id
WHERE eod.executive_id = 3
GROUP BY s.id
我添加了其余的主键。查询从9秒到2秒。
然后我将引用其他表的主键的字段设置为索引字段。查询从2秒到20秒，我分配了太多索引吗？
有什么方法可以加快这个速度？
答案 0 :(得分：1)
1。设置索引等后，您可以通过限制JOIN条件来加快速度。例如，而不是
LEFT JOIN uploads u ON s.id = u.summary_i
DO
LEFT JOIN uploads u ON (s.id = u.summary_i AND s.id = 3)
在所有表已加入后， 评估WHERE子句。尽可能预先确定JOIN条件。
2。您是否尝试从您的选择中构建视图并执行SELECT * FROM myView WHERE myView.id = 3？
更新：阅读this blog comment。