Question

我有一个具有以下结构的表：

timestamp, tagid, value

我想要一个查询，我只能收到标签ID列表的最新时间戳值。例如：

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

将返回整个值集。我只想要每个存储的最新值。

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

这个怎么样：

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)

仅返回时间戳表中的最新值

2 个答案: