Selecting the smallest value in one column per group - sql-server

Question

I have a table that looks like the following which was created using the following code...
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
I'd like to add to this code which would select the smallest Time_to_complete value per subject ID. Leaving the desired table:
ID Time_to_complete ... .....
1 5
2 6
3 7
4 14
I'm using Access and prefer to continue using Access to finish this code but I do have the option to use SQL Server if this is not possible in Access. Thanks!

Answer 1

I suspect you need correlated subquery :
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 . . .
);
EDIT : If you want unique records then you can do instead :
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 is your identity column that specifies unique entry in Orders table, so you can change it accordingly.

Answer 2

Have a look at 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);
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;
Results :
ID Time_to_complete
----------- ----------------
1 5
2 6
3 7
4 14
It uses row numbers over groups, then selects the first row for each group. You should be able to adjust your code to use this technique. If in doubt wrap your entire query in a cte first then apply the technique here.
It's worth becoming familiar with this process as it gets used in a lot of places - especially around de-duping data.

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