[英]MySQL Selecting rows while grouping by multiple columns with a condition
I have a table of events.我有一个事件表。 A host can create multiple events on a single day.
主持人可以在一天内创建多个事件。 Some of the events are recurring and some are not.
有些事件会重复发生,有些则不会。 I have a complex (for me) SELECT statement that I think requires conditionals some how and perhaps a subquery and I don't really know how to approach it.
我有一个复杂的(对我来说) SELECT 语句,我认为它需要一些条件,也许是一个子查询,但我真的不知道如何处理它。
Select Priority:选择优先级:
Here is a sample Events table:这是一个示例事件表:
+----+--------+---------+------------+-----------+
| id | hostid | title | start_date | recurring |
+----+--------+---------+------------+-----------+
| 1 | 1 | Event1A | 2016-10-01 | 1 |
| 2 | 1 | Event1B | 2016-10-01 | 0 |
| 3 | 1 | Event1C | 2016-10-02 | 0 |
| 4 | 1 | Event1D | 2016-10-02 | 1 |
| 5 | 1 | Event1E | 2016-10-02 | 1 |
| 6 | 1 | Event1F | 2016-10-03 | 1 |
| 7 | 1 | Event1G | 2016-10-03 | 1 |
| 8 | 1 | Event1H | 2016-10-04 | 1 |
| 9 | 1 | Event1I | 2016-10-05 | 0 |
| 10 | 2 | Event2A | 2016-10-01 | 1 |
| 11 | 2 | Event2B | 2016-10-01 | 0 |
| 12 | 2 | Event2C | 2016-10-02 | 1 |
| 13 | 2 | Event2D | 2016-10-03 | 0 |
+----+--------+---------+------------+-----------+
Here are my desired Results:这是我想要的结果:
+----+--------+---------+------------+-----------+
| id | hostid | title | start_date | recurring |
+----+--------+---------+------------+-----------+
| 2 | 1 | Event1B | 2016-10-01 | 0 |
| 3 | 1 | Event1C | 2016-10-02 | 0 |
| 6 | 1 | Event1F | 2016-10-03 | 1 |
| 7 | 1 | Event1G | 2016-10-03 | 1 |
| 8 | 1 | Event1H | 2016-10-04 | 1 |
| 9 | 1 | Event1I | 2016-10-05 | 0 |
| 11 | 2 | Event2B | 2016-10-01 | 0 |
| 12 | 2 | Event2C | 2016-10-02 | 1 |
| 13 | 2 | Event2D | 2016-10-03 | 0 |
+----+--------+---------+------------+-----------+
Here is a SQL Fiddle link with the table:这是带有该表的 SQL Fiddle 链接:
http://sqlfiddle.com/#!9/6427e/6 http://sqlfiddle.com/#!9/6427e/6
The task is rather simple: You want the record(s) with the minimum recurring flag per host and date.任务相当简单:您需要每个主机和日期具有最少重复标记的记录。
select events.*
from
(
select hostid, start_date, min(recurring) as recurring
from events
group by hostid, start_date
) chosen
join events on events.hostid = chosen.hostid
and events.start_date = chosen.start_date
and events.recurring = chosen.recurring
order by events.id;
Here is your SQL fiddle back: http://sqlfiddle.com/#!9/6427e/59 :-)这是你的 SQL 小提琴: http : //sqlfiddle.com/#!9/ 6427e/59 :-)
A friend helped me find this solution:一个朋友帮我找到了这个解决方案:
SELECT e.*
FROM Events e
LEFT JOIN (
SELECT start_date,
hostid,
count(*) cnt,
AVG(Cast(recurring as decimal)) recur
FROM Events
GROUP BY start_date, hostid
) r
ON e.start_date = r.start_date
AND e.hostid = r.hostid
WHERE (e.recurring = 0 and r.recur <> 1)
OR r.recur = 1 OR r.cnt = 1
ORDER BY e.id
http://sqlfiddle.com/#!9/6427e/65 http://sqlfiddle.com/#!9/6427e/65
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