Select min(value) form each day

I have the following table

date_time, data_value

date_time               data_value
----------------------- ----------------------
2011-03-28 15开发者_Python百科:05:29.000 20  
2011-03-28 15:55:39.000 40  
2011-03-28 16:25:45.000 30

2011-03-28 23:37:11.000 10  
2011-03-29 04:43:12.000 44  
2011-03-29 05:13:18.000 55  
2011-03-29 05:28:21.000 52  
2011-03-29 05:48:25.000 23  
2011-03-29 06:13:30.000 8  
2011-03-29 07:03:40.000 34  
2011-03-29 08:34:01.000 25  
2011-03-29 09:34:20.000 35  
2011-03-29 09:49:23.000 23  
2011-03-30 16:00:55.000 20

I would like to get the minimum value of each date in sql:

2011-03-29 06:13:30.000 8  
2011-03-28 15:05:29.000 20

any suggestions?

In SQL Server 2005+:

WITH ranked AS (
  SELECT
    date_time,
    data_value,
    rownum = ROW_NUMBER() OVER (
      PARTITION BY DATEADD(day, DATEDIFF(day, 0, date_time), 0)
      ORDER BY data_value
    )
  FROM atable
)
SELECT
  date_time,
  data_value
FROM ranked
WHERE rownum = 1

Something like

  select TO_DAYS(date_time) as dt,  min(date_time) from xxx group by dt;

Try those :

SELECT FROM_DAYS(TO_DAYS(data_time)) AS dt, min(data_value) FROM table GROUP BY TO_DAYS(NOW())

SELECT DATE_FORMAT(data_time,'YYY-MM-01') AS dt, min(data_value) FROM table GROUP BY dt

Does this work?

SELECT date_time, MIN(data_value)
FROM TABLE
GROUP BY date_time

Oh sorry now you've formatted the data that clearly isn't going to work! You'll need to apply a function to date_time, to cut out the just the Date and ignore the time portion.

In MySQL (and others e.g. DB2) you would do:

   SELECT DATE(date_time), MIN(data_value)
    FROM TABLE
    GROUP BY DATE(date_time)

For SQL Server this looks like it should work, please can someone verify:

SELECT CONVERT(varchar(10), date_time), MIN(data_value)
FROM TABLE
GROUP BY CONVERT(varchar(10), date_time)

Try this

select min(val),substring(date,1,10) from table group by substring(date,1,10)

 SELECT (ord_date), min([qty])

      FROM [pubs].[dbo].[sales]

     group by [ord_date]

     order by ord_date

select d(date_time), min(data_value)
from table
group by d(date_time)

where d is a function that extracts the date part from a date_time. (check your SQL reference manual for the function name).

In Oracle SQL that function is trunc.