[英]MySQL Selecting rows while grouping by multiple columns with a condition
我有一個事件表。 主持人可以在一天內創建多個事件。 有些事件會重復發生,有些則不會。 我有一個復雜的(對我來說) SELECT 語句,我認為它需要一些條件,也許是一個子查詢,但我真的不知道如何處理它。
選擇優先級:
這是一個示例事件表:
+----+--------+---------+------------+-----------+
| 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 |
+----+--------+---------+------------+-----------+
這是我想要的結果:
+----+--------+---------+------------+-----------+
| 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 |
+----+--------+---------+------------+-----------+
這是帶有該表的 SQL Fiddle 鏈接:
任務相當簡單:您需要每個主機和日期具有最少重復標記的記錄。
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;
這是你的 SQL 小提琴: http : //sqlfiddle.com/#!9/ 6427e/59 :-)
一個朋友幫我找到了這個解決方案:
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
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