Select values from multiple rows from 1 table as 1 record - sql

Question

I'm struggling to even explain what I need to do so please be patient with me.
I have the following table and rows in it:
TBNAME: Distances
Track, Person, Date, Distance
TRACK1, P1, 1/1/2014, 15
TRACK2, P1, 13/1/2014, 12
TRACK1, P1, 20/2/2014, 10
TRACK2, P1, 15/1/2014, 9
TRACK1, P2, 2/1/2014, 11
TRACK2, P2, 14/1/2014, 13
TRACK1, P2, 21/2/2014, 8
TRACK2, P2, 16/1/2014, 6
What I would, ideally, like to see as a result is something like this:
P1, TRACK1, 20/2/2014, 10, TRACK2, 15/1/2014, 9
P2, TRACK1, 21/2/2014, 8, TRACK2, 16/1/2014, 6
Or, in other words, for each person, the most recent date and distance for that date for each track in one row.
Hope someone can understand this and offer a solution too :)
Cheers,
Pierre

Answer 1

Try this:
SELECT T1.Person, T1.Track, MAX(T1.Date), MIN(T1.Distance),
T2.Track, MAX(T2.Date), MIN(T2.Distance)
FROM Distances AS T1 INNER JOIN
Distances AS T2 ON T1.Person = T2.Person
WHERE T1.Track <> T2.Track AND T1.Track = 'Track1'
GROUP BY T1.Track, T1.Person, T2.Track
The output result of the query is showing exactly the same of your expected result.

Answer 2

Try combining the table by itself and connecting them with the common column.
In your case you want Person.
Select t1.Person,
t1.Tract,
t1.Date,
t1.Distance,
t2.Tract,
t2.date,
t2.Distance
From table_name t1, table_name t2
WHERE t1.Person = t2.Person;

Answer 3

Try this:
SELECT DISTINCT ON ("Person", "Track") *
FROM "Table"
ORDER BY "Person", "Date" DESC NULLS LAST;

Answer 4

Here is a query to get the records needed. First get the maximum date per track and person. Then join with the table to get the complete record.
If you know beforehand which tracks you will get, you can use a pivot query for this. As I've never done this, I ask you to look this up yourself. However, as mentioned in my comment to your request, I would use a programming language (C#, Java, PHP or whatever) to care about that.
select d.track, d.person, d.date, d.distance
from
(
select track, person, max(distances.date) as `date`
from distances
group by track, person
) lastd
inner join distances d on d.track = lastd.track and d.person = lastd.person and d.date = lastd.date
order by d.track, d.person;
BTW: date is a reserved keyword. I would not recommend to use it for a column name. Whenever you use it without a qualifier you will have to use those strange quotes.

Answer 5

Look for ROW_NUMBER() and OVER PARITION BY.
Idea is something like (I did not try to run this query):
;WITH
data AS
(
SELECT
*,
-- returns number for each pair of person and track starting from most recent date
--Code enhanced at here
row_number() over (partition BY person, track order by dte DESC) nr
FROM distances
)
SELECT
*
FROM
data
WHERE
nr = 1 -- we want just the most recent one
ORDER BY
person, -- "group by" person
track ;
It's still doesn't support showing one row for each person...
I don't think you can do it with SQL (because of unknown number of tracks).
There is PIVOT/UNPIVOT, but I don't think it fits here.

Answer 6

WITH CTE AS
(
Select P1.Track,P1.Person,ROW_NUMBER() OVER (Partition by Person,Track Order by Date
Desc) AS RN1
,Date,Distance
from Distances P1
)Select T.Person,T.Track1,T.T1Date
,T.T1Distance,T.Track2,T.T2Date,T.T2Distance
From (
Select C1.Person,C1.Track AS 'Track1',C1.Date AS 'T1Date',
C1.Distance 'T1Distance',
C2.Track AS 'Track2',C2.Date As 'T2Date',C2.Distance 'T2Distance',
ROW_NUMBER() OVER (Partition BY C1.Person Order by C1.Date Desc) RNX
from
CTE C1
JOIN
CTE C2 ON C1.RN1=1 AND C2.RN1=1
AND C1.Person=C2.Person
AND C1.Track<>C2.Track
)t Where t.RNX=1

Answer 7

you may also use dynamic query to achieve your expected result :)
DECLARE #nCount INT
DECLARE #nStart INT
DECLARE #Query NVARCHAR(MAX) =' '
DECLARE #sPerson NVARCHAR(MAX)
DECLARE #sTrack NVARCHAR(MAX)
SET #nCount = (SELECT COUNT(DISTINCT(person)) FROM DISTANCES)
SET #nStart = 1
WHILE #nStart <= #nCount
BEGIN
SET #sPerson = (SELECT PERSON FROM (
SELECT PERSON, ROW_NUMBER() OVER (ORDER BY PERSON) RN FROM (
SELECT DISTINCT(PERSON) FROM DISTANCES
) T1
) T2 WHERE RN = #nStart
)
SET #Query = #Query + '
SELECT '''+#sPerson+''' + '','' + STUFF( '','' +(
SELECT TRACK + '', '' + DATE + '', '' + DISTANCE FROM (
SELECT TRACK, DATE,DISTANCE,
ROW_NUMBER() OVER (PARTITION BY TRACK ORDER BY DATE DESC) RN FROM (
SELECT TRACK,date,DISTANCE FROM DISTANCES WHERE PERSON = '''+#sPerson+'''
) T1
) T2
WHERE RN = 1 FOR XML PATH('''')
),1,1,''''
)
'
IF(#nStart != #nCount)
SET #Query = #Query + ' UNION ALL '
SET #nStart = #nStart + 1
END
EXEC SP_EXECUTESQL #Query

Answer 8

To have a general query it need to be dynamic
DECLARE #query AS NVARCHAR(MAX)
DECLARE #pivotCols AS NVARCHAR(MAX)
DECLARE #cols AS NVARCHAR(MAX)
SELECT #pivotCols = STUFF((SELECT DISTINCT ',' + QUOTENAME([Track])
FROM Distances
FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)') , 1, 1, '')
;WITH T AS (
SELECT Track
, _ID = CAST(Row_Number() OVER (ORDER BY Track) AS VARCHAR)
FROM Distances
GROUP BY Track
)
SELECT #Cols = STUFF((
SELECT ', Track_' + _ID + ' = ''' + Track + ''''
+ ', LastRun_' + _ID + ' = ' + QUOTENAME([Track])
+ ', Distance_' + _ID + '
= SUM(CASE WHEN d.Date = ' + QUOTENAME([Track]) + '
AND d.Track = ''' + Track + '''
THEN d.Distance ELSE NULL END)'
FROM T FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)') , 1, 1, '')
SELECT #query = '
With LR AS (
SELECT Person, ' + #pivotCols + '
FROM (SELECT Track, Person, [Date] FROM Distances) d
PIVOT (MAX([Date]) FOR Track IN (' + #pivotCols + ')) pvt
)
SELECT d.Person, ' + #Cols + '
FROM Distances d
INNER JOIN LR ON d.Person = LR.Person AND d.Date IN (' + #pivotCols + ')
GROUP BY d.Person, ' + #pivotCols + ''
execute(#query);
SQLFiddle demo
The first query generate the list of field for the PIVOT.
The second one generate the fields for the compound query.
The PIVOT is used to get, for every person, the last run on every track, that is than joined back to the base data to get the distance