[英]MySQL: Select several rows based on several keys from two different tables
我有这两个表user_schedules
和user_schedule_meta
,如下所示:
------------------------------------
| id | scheduler_id | status |
------------------------------------
1 3 pending
2 5 active
3 6 active
和
----------------------------------------------
| id | user_schedule_id | meta_key |meta_value
----------------------------------------------
1 3 course-id 135
2 3 session-id 15
3 3 schedule-id 120
我想编写一个查询,使我能够从满足以下5个条件中每个人的两个表中进行选择:
这是我到目前为止的内容,但是没有用:
SELECT user_schedule_meta.`id` FROM user_schedule_meta, user_schedules
WHERE user_schedules.`scheduler_id` = 6
AND user_schedules.id = user_schedule_meta.`user_schedule_id`
AND (
(user_schedule_meta.`meta_key` = 'course-id' AND user_schedule_meta.`meta_value` = 135)
OR (user_schedule_meta.`meta_key` = 'session-id' AND user_schedule_meta.`meta_value` = 15)
OR (user_schedule_meta.`meta_key` = 'daily-schedule-id' AND user_schedule_meta.`meta_value` = 120)
)
GROUP BY user_schedule_meta.`id`
有什么建议我做的不对吗?
这是典型的键值存储查找问题。 这些比在SQL中看起来要棘手,因为它们需要多个JOIN操作。
您需要一个虚拟表,其中每个user_schedules.id
值都有一行,然后可以对其进行过滤。 所以
SELECT u.id, u.scheduler_id
FROM user_schedules u
JOIN user_schedule_meta a ON u.id=a.user_schedule_id AND a.meta_key='course-id'
JOIN user_schedule_meta b ON u.id=b.user_schedule_id AND b.meta_key='session-id'
JOIN user_schedule_meta c ON u.id=c.user_schedule_id AND c.meta_key='daily-schedule-id'
WHERE a.meta_value = 135 -- value associated with course-id
AND b.meta_value=15 -- value associated with session-id
AND c.meta_value=120 -- value associated with daily-schedule-id
还要注意,您可以像这样列出具有关联属性的表。 多次连接键/值表的技巧是一种透视操作。 我使用LEFT JOIN,因为它将允许结果集显示缺少属性的行。
SELECT u.id, u.scheduler_id, u.status,
a.meta_value AS course_id,
b.meta_value AS session_id,
c.meta_value AS daily_schedule_id
FROM user_schedules u
LEFT JOIN user_schedule_meta a ON u.id=a.user_schedule_id AND a.meta_key='course-id'
LEFT JOIN user_schedule_meta b ON u.id=b.user_schedule_id AND b.meta_key='session-id'
LEFT JOIN user_schedule_meta c ON u.id=c.user_schedule_id AND c.meta_key='daily-schedule-id'
试试这是代码
select * from user_schedule_meta where user_schedule_id=3 and
(meta_key='session-id' AND meta_value=15
or meta_key='daily-schedule-id' AND meta_value=120
or meta_key='course-id' AND meta_value=135
)
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