T-SQL，按一列分组，取两列最大值

Question

我想 select 每个 ID 的最高价格，但只有具有最高 lastupdated 列的行的价格。

使用此查询不会给我正确的价格。

SELECT 
    id, MAX(price) as price, MAX(lastupdated) as lastupdated 
FROM 
    tbl 
GROUP BY 
    id

样本表数据：

id, price, lastupdated
1, 50, 2015-03-01
1, 51, 2015-03-01
1, 52, 2015-03-01
1, 53, 2015-02-28
1, 54, 2015-02-28
1, 55, 2015-02-28
2, 20, 2015-02-01
2, 21, 2015-02-01
2, 22, 2015-02-01
2, 33, 2015-01-28
2, 34, 2015-01-28
2, 35, 2015-01-28

我想要的结果是：

id, price, lastupdated
1, 52, 2015-03-01
2, 22, 2015-02-01

Answer 1

您可以使用过滤 join 只查看具有最新日期的行：

SELECT  tbl.id
,       MAX(price) as price
,       lastupdated 
FROM    Tel
JOIN    (
        SELECT  id
        ,       MAX(last_updated) as maxupdated
        FROM    tbl
        GROUP BY
                id
        ) mx
ON      tbl.id = mx.id
        AND tbl.lastupdated = mx.maxupdated
GROUP BY 
        tbl.id
,       last_updated

Answer 2

您需要找到每个 id 的 lastupdated 并加入：

SELECT tbl.id, MAX(price) as price, m.lastupdated
FROM tbl 
JOIN (
    SELECT id, MAX(lastupdated) AS lastupdated 
    FROM tbl 
    GROUP BY id
) m ON tbl.id = m.id and tbl.lastupdated = m.lastupdated
GROUP BY tbl.id, m.lastupdated
ORDER BY tbl.id

Answer 3

您可以使用 RANK 为您 table 的每条记录分配一个排名编号。然后在外部查询中使用此数字 select 具有每个 id 的最新 lastupdated 值的所有记录：

SELECT id, MAX(price) as price, lastupdated
FROM (
   SELECT id, price, lastupdated,
          RANK() OVER (PARTITION BY id ORDER BY lastupdated DESC) AS rnk
   FROM tbl ) t  
WHERE t.rnk = 1 
GROUP BY id, lastupdated

或者，您可以使用 HAVING 子句过滤掉任何 (id, lastupdated) 没有最大 lastupdated 日期值的组：

SELECT id, MAX(price) as price, lastupdated
FROM #tbl t1
GROUP BY id, lastupdated
HAVING lastupdated = (SELECT MAX(lastupdated) FROM #tbl t2 WHERE id = t1.id)

使用 HAVING 子句的查询更简洁但效率较低，因为它使用的子查询 (SELECT MAX(lastupdated) ...) 对每个组 计算一次 在外部查询中定义。

Answer 4

今天觉得cte是个不错的方法

with cte ( id, maxdate )
as
(
  select id, max(lastupdated)
  from tbl
  group by id
)
select 
     t3.id
    ,max(price)
    ,max(maxdate)
from 
    tbl t3 
        inner join cte on t3.id = cte.id and t3.lastupdated = cte.maxdate
group by
    t3.id

T-SQL，按一列分组，取两列最大值

T-SQL, get highest values from two columns while grouping by one column

tsql

sql-server