Sql: How to Select a Max Value for Each Group Per Day

Get max value per day with the corresponding name

Use distinct on:

select distinct on (day) t.*
from t
order by day, val desc;

SQL select issue : get max value for each day

You already use GROUP BY the distinct is no make sense, so the distinct can be removed.

then you just modify CONVERT(Date,attemptdate) instead of attemptdate in Group by, and only need to group by CONVERT(Date,attemptdate)

select CONVERT(Date,attemptdate) as Date, max(currentcount) as MAXUSERS
from logintracking 
where attemptdate between @dateDebut and @dateFin
  and logintracking.clientaddr in ('10.118.254.21', '10.118.254.156') 
group by CONVERT(Date,attemptdate)

Note:

Your @dateDebut and @dateFin already are Date type. No need to use CONVERT function.

Get records with max value for each group of grouped SQL results

There's a super-simple way to do this in mysql:

select * 
from (select * from mytable order by `Group`, age desc, Person) x
group by `Group`

This works because in mysql you're allowed to not aggregate non-group-by columns, in which case mysql just returns the first row. The solution is to first order the data such that for each group the row you want is first, then group by the columns you want the value for.

You avoid complicated subqueries that try to find the max() etc, and also the problems of returning multiple rows when there are more than one with the same maximum value (as the other answers would do)

Note: This is a mysql-only solution. All other databases I know will throw an SQL syntax error with the message "non aggregated columns are not listed in the group by clause" or similar. Because this solution uses undocumented behavior, the more cautious may want to include a test to assert that it remains working should a future version of MySQL change this behavior.

Version 5.7 update:

Since version 5.7, the sql-mode setting includes ONLY_FULL_GROUP_BY by default, so to make this work you must not have this option (edit the option file for the server to remove this setting).

find single MAX value per day

You dont tell us what SQL product your using, so here is Sql Server 2008R2:

SELECT
CAST(t.DateColumn as DATE), MAX(t.PowerUsage) as 'Peak Power Each Day'
FROM [MyTable] t
GROUP BY CAST(t.DateColumn AS DATE)

here is MySql

SELECT
DATE(t.DateColumn), MAX(t.PowerUsage) as 'Peak Power Each Day'
FROM [MyTable] t
GROUP BY DATE(t.DateColumn)

GROUP BY with MAX(DATE)

You cannot include non-aggregated columns in your result set which are not grouped. If a train has only one destination, then just add the destination column to your group by clause, otherwise you need to rethink your query.

Try:

SELECT t.Train, t.Dest, r.MaxTime
FROM (
      SELECT Train, MAX(Time) as MaxTime
      FROM TrainTable
      GROUP BY Train
) r
INNER JOIN TrainTable t
ON t.Train = r.Train AND t.Time = r.MaxTime

Show only the max value of each group

If you just want the max amount, with respect to the date- you can take the MAX and cast the datetime as a date:

DECLARE @temp TABLE (groupno int, [user] varchar(20), status varchar(20), date datetime, amount int)

INSERT INTO @temp
VALUES
 (74,'user1', 'status_1', '2016-01-01 05:40:00.0', 900)
,(74,'user1', 'status_1', '2016-01-01 05:45:00.0', 1200)
,(79,'user1', 'status_2', '2016-01-01 05:45:31.0', 31)
,(79,'user1', 'status_2', '2016-01-01 05:50:00.0', 300)
,(79,'user1', 'status_2', '2016-01-01 05:55:00.0', 600)
,(79,'user1', 'status_2', '2016-01-01 06:00:00.0', 900)
,(79,'user1', 'status_2', '2016-01-01 06:05:00.0', 1200)
,(90,'user1', 'status_1', '2016-01-01 06:07:52.0', 172)
,(90,'user1', 'status_1', '2016-01-01 06:10:00.0', 300)
,(90,'user1', 'status_1', '2016-01-01 06:15:00.0', 600)

SELECT groupno, [user], [status], CAST([date] as date) [Date], MAX(amount) as MAXamount
FROM @temp
GROUP BY groupno, [user], [status], CAST([date] as date)

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