SQL 从查询结果中删除重复项

Question

这是我的 SQL :

 SELECT * FROM unity_database.unit_uptime_daily
        inner join unity_database.units on unity_database.units.id = unity_database.unit_uptime_daily.unit_id
        where unity_database.units.location_id = 1

下面是第一部分结果的截图：

我试图只为每个具有最新日期的 unit_id 显示一个结果，所以在这个例子中，unit_id 为 30 的单位应该只显示一次，它应该是最后一行。

有什么想法吗？

Answer 1

WITH X AS
(
SELECT * 
       ,ROW_NUMBER() OVER (PARTITION BY Unit_Id ORDER BY [Timestamp] DESC) rn
FROM unity_database.unit_uptime_daily
inner join unity_database.units 
on unity_database.units.id = unity_database.unit_uptime_daily.unit_id
where unity_database.units.location_id = 1
)
SELECT * FROM X Where rn = 1

或

SELECT * 
FROM (
    SELECT * 
           ,ROW_NUMBER() OVER (PARTITION BY Unit_Id ORDER BY [Timestamp] DESC) rn
    FROM unity_database.unit_uptime_daily
    inner join unity_database.units 
    on unity_database.units.id = unity_database.unit_uptime_daily.unit_id
    where unity_database.units.location_id = 1
     )A
WHERE rn = 1

Answer 2

这里有一个 MySQL 您可以考虑的解决方案：

SELECT t1.id, t1.unit_id, t1.uptime, t1.total_update, t2.timestamp
FROM
(
    SELECT *
    FROM unity_database.unit_uptime_daily ud1 INNER JOIN unity_database.units ud2
        ON ud2.id = ud1.unit_id
    WHERE ud2.location_id = 1
) t1
INNER JOIN
(
    SELECT ud1.unit_id, MAX(ud1.timestamp) AS timestamp
    FROM unity_database.unit_uptime_daily ud1 INNER JOIN unity_database.units ud2
        ON ud2.id = ud1.unit_id
    WHERE ud2.location_id = 1
    GROUP BY ud1.unit_id
) t2
ON t1.unit_id = t2.unit_id AND t1.timestamp = t2.timestamp

Answer 3

如果这个答案能给您带来您期望的结果，请：

 SELECT MAX(id) AS ID, unit_id, uptime, total_update, MAX(timestamp) as timesstamp FROM unity_database.unit_uptime_daily
    inner join unity_database.units on unity_database.units.id = unity_database.unit_uptime_daily.unit_id
 where unity_database.units.location_id = 1
 GROUP BY unit_id, uptime, total_update

PS：我没有测试，但我肯定它会起作用

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