SQL Statement to Get The Minimum DateTime from 2 String FIelds - sql

Question

I've got a bit of a messy table on my hands that has two fields, a date field and a time field that are both strings. What I need to do is get the minimum date from those fields, or just the record itself if there is no date/time attached to it. Here's some sample data:
ID First Last Date Time
1 Joe Smith 2013-09-06 04:00
1 Joe Smith 2013-09-06 02:00
2 Jack Jones
3 John Jack 2013-09-05 06:00
3 John Jack 2013-09-15 15:00
What I would want from a query is to get the following:
ID First Last Date Time
1 Joe Smith 2013-09-06 02:00
2 Jack Jones
3 John Jack 2013-09-05 06:00
The min date/time for ID 1 and 3 and then just ID 2 back because he doesn't have a date/time. I cam up with the following query that gives me ID's 1 and 3 exactly as I would want them:
SELECT *
FROM test as t
where
cast(t.date + ' ' + t.time as Datetime ) = (select top 1 cast(p.date + ' ' + p.time as Datetime ) as dtime from test as p where t.ID = p.ID order by dtime)
But it doesn't return row number 2 at all. I imagine there's a better way to go about doing this. Any ideas?

Answer 1

You can do this with row_number():
select ID, First, Last, Date, Time
from (select t.*,
row_number() over (partition by id order by date, time) as seqnum
from test t
) t
where seqnum = 1;
Although storing dates and times as strings is not recommended, you at least do it right. The values use the ISO standard format (or close enough) so alphabetic sorting is the same as date/time sorting.

Answer 2

Assuming [Date] and [Time] are the types I think they are, and not strings:
SELECT ID,[First],[Last],[Date],[Time] FROM
(
SELECT ID,[First],[Last],[Date],[Time],rn = ROW_NUMBER()
OVER (PARTITION BY ID ORDER BY [Date], [Time])
FROM dbo.test
) AS t WHERE rn = 1;
Example:
DECLARE #x TABLE
(
ID INT,
[First] VARCHAR(32),
[Last] VARCHAR(32),
[Date] DATE,
[Time] TIME(0)
);
INSERT #x VALUES
(1,'Joe ','Smith','2013-09-06','04:00'),
(1,'Joe ','Smith','2013-09-06','02:00'),
(2,'Jack','Jones',NULL, NULL ),
(3,'John','Jack ','2013-09-05','06:00'),
(3,'John','Jack ','2013-09-15','15:00');
SELECT ID,[First],[Last],[Date],[Time] FROM
(
SELECT ID, [First],[Last],[Date],[Time],rn = ROW_NUMBER()
OVER (PARTITION BY ID ORDER BY [Date], [Time])
FROM #x
) AS x WHERE rn = 1;
Results:
ID First Last Date Time
-- ----- ----- ---------- --------
1 Joe Smith 2013-09-06 02:00:00
2 Jack Jones NULL NULL
3 John Jack 2013-09-05 06:00:00

Answer 3

Try:
SELECT
*
FROM
test as t
WHERE
CAST(t.date + ' ' + t.time as Datetime) =
(
select top 1 cast(p.date + ' ' + p.time as Datetime ) as dtime
from test as p
where t.ID = p.ID
order by dtime
)
OR (t.date='' AND t.time='')