用MySQL檢索第一個和最後一個小時的條目

Question

我有數據庫來存儲溫度。每小時有三到五個溫度，我想得到一個小時的第一個和最後一個溫度，但是我無法創建合適的子查詢。

下面是按小時計算溫度的主要查詢。

SELECT HOUR(time) AS h, max(temp_in) as max, min(temp_in) as min, count(temp_in) as count 
FROM tbl_temps 
GROUP BY h; 

Answer 1

您可以使用一個工會和子查詢

select * from 
my_table where (HOUR(time),MINUTE(time)) in (
     select HOUR(time), min(MINUTE(time)) 
     from my_table 
     group by HOUR(time) 
) 
union 
select * from 
my_table where (HOUR(time),MINUTE(time)) in (
     select HOUR(time), max(MINUTE(time)) 
     from my_table 
     group by HOUR(time) 
) 
order by HOUR(time), MINUTE(time)