私のテーブルには、次のようになります:T-SQLは、最後の日付時刻レコード
+---------+------------------------+-------+---------+---------+
|channel |date |code |comment |order_id |
+---------+------------------------+-------+---------+---------+
|1 |2017-10-27 12:04:45.397 |2 |comm1 |1 |
|1 |2017-10-27 12:14:20.997 |1 |comm2 |1 |
|2 |2017-10-27 12:20:59.407 |3 |comm3 |1 |
|2 |2017-10-27 13:14:20.997 |1 |comm4 |1 |
|3 |2017-10-27 12:20:59.407 |2 |comm5 |1 |
|3 |2017-10-27 14:20:59.407 |1 |comm6 |1 |
+---------+------------------------+-------+---------+---------+
そして、私はこのような結果を期待:
+---------+------------------------+-------+---------+
|channel |date |code |comment |
+---------+------------------------+-------+---------+
|1 |2017-10-27 12:14:20.997 |1 |comm2 |
|2 |2017-10-27 13:14:20.997 |1 |comm4 |
|3 |2017-10-27 14:20:59.407 |1 |comm6 |
+---------+------------------------+-------+---------+
必ず1枚のORDER_ID = xでのレコードとの最大の日付各チャンネルチャネルの総数は一定です。 私のクエリは機能しますが、テーブルが成長するにつれてパフォーマンスが心配です。 3つのほとんど同じクエリを実行することは賢明ではないようです。
select
*
from
(select top(1)
channel,
date,
code,
comment
from
status
where
channel = 1 and
order_id = 1 and
cast(date as date) = '2017-10-27'
order by
date desc) channel1
union
select
*
from
(select top(1)
channel,
date,
code,
comment
from
status
where
channel = 2 and
order_id = 1 and
cast(date as date) = '2017-10-27'
order by
date desc) channel2
union
select
*
from
(select top(1)
channel,
date,
code,
comment
from
status
where
channel = 3 and
order_id = 1 and
cast(date as date) = '2017-10-27'
order by
date desc) channel3
これを改善するにはどうすればよいですか?
[T-SQL:MAX(他の列)に基づいて選択するコラム】の可能な重複(https://stackoverflow.com/questions/3680254/t-sql-selecting-column-based-on-maxother -column) –