MYSQL - GROUP BY 2 COLUMN ORDER BY創建日期

Question

我想通過2列的GROUP BY獲取我的表的所有結果並獲取最後一次插入。

「價格」 表：

我的要求：

SELECT DISTINCT p.* 
FROM prices p 
JOIN (
SELECT MAX(created_at) as "last_created" 
FROM prices 
WHERE station_id = 27210003 
GROUP BY station_id, fuel_id) as sub 
ON sub.last_created = p.created_at 
WHERE p.station_id = 27210003 
GROUP BY p.station_id, p.fuel_id 

結果是3線，但錯了行，因爲不是我的數據庫最後創建-_-」

請幫幫我!!! > _ <'

THX

Answer 1

既然你的WHERE子句中選擇特定station_id，你並不需要包括在GROUP BY。

子查詢必須返回要分組的列，然後必須將它們包含在ON子句中。

而且你不需要GROUP BY在外部查詢，因爲JOIN應確保有隻有一行每個fuel_id（除非有相同fuel_id和station_id重複created_at）。

SELECT DISTINCT p.* 
FROM prices p 
JOIN (
    SELECT fuel_id, MAX(created_at) as "last_created" 
    FROM prices 
    WHERE station_id = 27210003 
    GROUP BY fuel_id) as sub 
ON sub.last_created = p.created_at AND sub.fuel_id = p.fuel_id 
WHERE p.station_id = 27210003