在连接包含BLOB的表时，MySQL查询很慢

Question

我有一个带有大量左连接的MySQL选择查询，但只有一个连接导致严重的性能问题。这个麻烦的表中有2个BLOB字段，当我在其主键上保持连接时，查询占用的时间超过20倍。由于这是唯一导致问题的表，我假设BLOB与它有关（即使它们没有被选中或加入）。请注意，此表中的行数相对于其他连接表而言并不是特别大。

如何加快此查询？

编辑 - 这是查询（有问题的表格是“提交”）：

SELECT
 actions.id,
 actions.facebook_id,
 actions.created_at,
 actions.current_total_points,
 actions.current_weekly_points,
 submissions.id AS submission_id,
 submissions.challenge_week_number AS submission_challenge_week_number,
 submissions.challenge_number_in_week AS submission_challenge_number_in_week,
 reward_events.id AS reward_event_id,
 reward_events.reward_event_type_id,
 reward_events.action_id,
 reward_events.awarded_badge_type_id,
 reward_events.for_week_number AS reward_event_for_week_number,
 reward_events.challenge_number_in_week AS reward_event_challenge_number_in_week,
 challenge_weeks.week_number
from actions
left join submissions ON submissions.action_id = actions.id
left join reward_events ON reward_events.action_id = actions.id
left join challenge_weeks ON challenge_weeks.start_date <= CAST(actions.created_at AS DATE) AND challenge_weeks.end_date >= CAST(actions.created_at AS DATE)
where actions.facebook_id = '12345678'
order by actions.id asc

以下是“提交”表格的EXPLAIN结果：

id                        bigint(11) unsigned           NO  PRI  auto_increment
action_id                 bigint(11)                    NO
title                     varchar(255)                  YES
description               varchar(255)                  YES
submission_type           enum('alpha','beta','gamma')  YES
filename                  varchar(255)                  YES
ip_address                varchar(255)                  YES
community_release         bit(1)                        YES
approved                  bit(1)                        YES
fullsize                  longblob                      YES
thumb                     longblob                      YES
modified_at               timestamp                     YES  CURRENT_TIMESTAMP  
challenge_week_number     tinyint(1)                    YES
challenge_number_in_week  tinyint(1)                    YES

Answer 1

您是否尝试在您加入的非PK字段上创建索引，例如submissions.action_id和reward_events.action_id？这应该会导致查询时间的减少与您加入的表的大小成比例。