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[英]SQL query to only return the rows that have the highest value in a certain column
[英]SQL Query return highest date value in query
我試圖運行查詢來執行以下操作:
返回給定日期范圍內表中的所有最新條目。
目前我正在使用此查詢
SELECT id FROM schedule WHERE eventdate BETWEEN '2014-09-01' AND '2014-09-07'
它返回下面顯示的計划表中的記錄1,2,3,4,5
時間表。
+----+------------+-------------+-----------------+------------+----------+ | id | eventdate | resource_id | text | added_on | added_by | +----+------------+-------------+-----------------+------------+----------+ | 1 | 2014-09-05 | 1 | Some old text | 2014-08-01 | Sam | | 2 | 2014-09-05 | 1 | Some newer text | 2014-09-01 | Jordan | | 3 | 2014-09-06 | 1 | another day | 2014-09-03 | Jordan | | 4 | 2014-09-05 | 1 | Most recent | 2014-09-10 | Jordan | | 5 | 2014-09-07 | 2 | Other resource | 2014-09-09 | Sam | +----+------------+-------------+-----------------+------------+----------+
我試圖只返回指定日期范圍內的唯一記錄,其中應返回的唯一記錄是在added_on
列中具有最高日期時間戳的added_on
。
在上面的例子中,我想只返回記錄3,4,5。 記錄1和2已被記錄4取代。
**請注意: added_on
列的類型為日期時間戳(yyyy-mm-dd HH:mm:ss),為清晰起見,已將其保留為**
我不知道查詢將返回的行數,確定記錄唯一性的信息是eventdate, resource_id and added_on
即,每天每個資源只應返回一條記錄,並且此記錄應具有最高的added_on值
SELECT s1.* FROM schedule s1
inner join (select max(id) as id1 from schedule WHERE eventdate BETWEEN '2014-09-01' AND '2014-09-07' group by eventdate,resource_id ) as s2 on s2.id1=s1.id
它會對你有用
你說你通過三列eventdate,resource_id和added_on來確定每一天的唯一性......但是你只想要每天最大的added_on ...所以不要按add_on .. group by eventdate分組來獲取白天的數據,按eventdate分組,resource_id按資源_id每天獲取數據。
嘗試獲取唯一ID,然后通過它們過濾外部查詢
SELECT *
FROM schedule
WHERE ID IN
( SELECT MAX(id)
FROM schedule
WHERE eventdate BETWEEN '2014-09-01' AND '2014-09-07'
GROUP BY eventdate, resource_id
)
或者如果你想使用最高的added_on,你可以用同樣的方式
SELECT *
FROM schedule
WHERE added_on IN
( SELECT MAX(added_on)
FROM schedule
WHERE eventdate BETWEEN '2014-09-01' AND '2014-09-07'
GROUP BY eventdate, resource_id
)
如果你想擺脫使用IN並使用JOIN,你可以在MAX()上添加一個JOIN來實現。
SELECT *
FROM schedule s
JOIN
( SELECT MAX(added_on) as added_on
FROM schedule
WHERE eventdate BETWEEN '2014-09-01' AND '2014-09-07'
GROUP BY eventdate, resource_id
) t ON t.added_on = s.added_on
您需要獲取eventdate,resource_id,added_on的每個唯一組合的最新記錄,如下所示:
SELECT schedule.*
FROM schedule JOIN (
SELECT MAX(id) AS max_id
FROM schedule
GROUP BY eventdate, resource_id, added_on
) t
ON t.max_id = schedule.id
WHERE eventdate BETWEEN '2014-09-01' AND '2014-09-07'
我認為這將是您可以擁有的最簡單的查詢。 如果您還有其他問題,請在此處發表評論
SELECT MAX(id) , eventdate, Max(added_on) FROM schedule GROUP BY eventdate.
這將返回
+----+------------+------------+
| id | eventdate | added_on |
+----+------------+------------+
| 3 | 2014-09-06 | 2014-09-03 |
| 4 | 2014-09-05 | 2014-09-10 |
| 5 | 2014-09-07 | 2014-09-09 |
+----+------------+------------+
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