每组选择一列中的最小值

Question

我有一个 table 看起来像下面的内容，它是使用以下代码创建的...

SELECT Orders.ID, Orders.CHECKIN_DT_TM, Orders.CATALOG_TYPE, 
Orders.ORDER_STATUS, Orders.ORDERED_DT_TM, Orders.COMPLETED_DT_TM, 
Min(DateDiff("n",Orders.ORDERED_DT_TM,Orders.COMPLETED_DT_TM)) AS 
Time_to_complete

FROM Orders

GROUP BY Orders.ORDER_ID, Orders.ID,
Orders.CHECKIN_DT_TM, Orders.CATALOG_TYPE, Orders.ORDERED_DT_TM, 
Orders.COMPLETED_DT_TM, HAVING (((Orders.CATALOG_TYPE)="radiology");

ID  Time_to_complete ... .....
1        5
1        7
1        8
2        23
2        6
3        7
4        16
4        14

我想在此代码中添加 select 每个主题 ID 的最小 Time_to_complete 值。留下想要的 table:

ID  Time_to_complete ... .....
1        5
2        6
3        7
4        14

我正在使用 Access，并且更愿意继续使用 Access 来完成此代码，但如果这在 Access 中不可行，我确实可以选择使用 SQL 服务器。谢谢！

Answer 1

我怀疑您需要 correlated 子查询 :

SELECT O.*, DateDiff("n", O.ORDERED_DT_TM, O.COMPLETED_DT_TM) AS Time_to_complete
FROM Orders O
WHERE DateDiff("n", O.ORDERED_DT_TM, O.COMPLETED_DT_TM) = (SELECT Min(DateDiff("n", O1.ORDERED_DT_TM, O1.COMPLETED_DT_TM))     
                                                           FROM Orders O1
                                                           WHERE O1.ORDER_ID = O.ORDER_ID AND . . . 
                                                          );

编辑：如果你想要唯一的记录，那么你可以这样做：

SELECT O.*, DateDiff("n", O.ORDERED_DT_TM, O.COMPLETED_DT_TM) AS Time_to_complete
FROM Orders O
WHERE o.pk = (SELECT TOP (1) o1.pk  
              FROM Orders O1
              WHERE O1.ORDER_ID = O.ORDER_ID AND . . . 
              ORDER BY DateDiff("n", O.ORDERED_DT_TM, O.COMPLETED_DT_TM) ASC
             );

pk 是您的身份列，它指定了 Orders table 中的唯一条目，因此您可以相应地更改它。

Answer 2

看看这个：

DECLARE @myTable AS TABLE (ID INT, Time_to_complete INT);

INSERT INTO @myTable
VALUES (1, 5)
,      (1, 7)
,      (1, 8)
,      (2, 23)
,      (2, 6)
,      (3, 7)
,      (4, 16)
,      (4, 14);

WITH cte AS
    (SELECT *
     ,      ROW_NUMBER() OVER (PARTITION BY ID  ORDER BY Time_to_complete) AS RN
       FROM @myTable)
SELECT  cte.ID
,       cte.Time_to_complete
  FROM  cte
 WHERE  RN = 1;

结果：

ID          Time_to_complete
----------- ----------------
1           5
2           6
3           7
4           14

它在组中使用行号，然后为每个组选择第一行。您应该能够调整您的代码以使用此技术。如果有疑问，请先将整个查询包装在一个 cte 中，然后在此处应用该技术。

值得熟悉这个过程，因为它被用在很多地方——尤其是在重复数据删除方面。

Answer 3

Try This 

    DECLARE @myTable AS TABLE (ID INT, Time_to_complete INT);

    INSERT INTO @myTable
    VALUES (1, 5)
    ,      (1, 7)
    ,      (1, 8)
    ,      (2, 23)
    ,      (2, 6)
    ,      (3, 7)
    ,      (4, 16)
    ,      (4, 14);


    SELECT  O.ID, O.Time_to_complete 
    FROM @myTable O
    WHERE o.Time_to_complete  = (Select min(m.Time_to_complete) FROM @myTable m
                                                        Where o.id=m.ID
                                                              );


Result :

ID  Time_to_complete
1   5
2   6
3   7
4   14

每组选择一列中的最小值

Selecting the smallest value in one column per group

sql-server

ms-access-2010