從時間戳表

Question

只返回最新值我有一個表結構如下：

timestamp, tagid, value 

我想查詢在那裏我可以爲標籤ID的列表只接收最新的時間戳值。例如：

SELECT * FROM floatTable WHERE tagid IN(1,2,3,4,5,6) 

將返回整組值。我只想爲每一個存儲最新的值。

Answer 1

select f.timestamp, f.tagid, f.value 
from floatTable f 
inner join (
    select tagid, max(timestamp) as timestampMax 
    from floatTable 
    where tagid in (1,2,3,4,5,6) 
    group by tagid 
) fm on f.tagid = fm.tagid and f.timestamp = fm.timestampMax 

Answer 2

如何：

select vt.tagid, maxdate, t.value 
from 
    ( 
    select tagid, max(timestamp) as maxdate 
    from floatTable 
    group by tagid 
) vt 
inner join floatTable t on t.tagid = vt.tagid 
where t.timestamp = vt.maxdate 
and t.tagid in (1,2,3,4,5,6)