SQL statement merge two rows into one - sql

Question

In the results of my sql-statement (SQL Server 2016) I would like to combine two rows with the same value in two columns ("study_id" and "study_start") into one row and keep the row with higest value in a third cell ("Id"). If any columns (i.e. "App_id" or "Date_arrival) in the row with higest Id is NULL, then it should take the value from the row with the lowest "Id".
I get the result below:
Id study_id study_start Code Expl Desc Startmonth App_id Date_arrival Efter_op Date_begin
167262 878899 954 4.1 udd.ord Afbrudt feb 86666 21-06-2012 N 17-08-2012
180537 878899 954 1 Afsluttet Afsluttet feb NULL NULL NULL NULL
And I would like to get this result:
Id study_id study_start Code Expl Desc Startmonth App_id Date_arrival Efter_op Date_begin
180537 878899 954 1 Afsluttet Afsluttet feb 86666 21-06-2012 N 17-08-2012
My statement looks like this:
SELECT dbo.PopulationStam_V.ELEV_ID AS id,
dbo.PopulationStam_V.PERS_ID AS study_id,
dbo.STUDIESTARTER.STUDST_ID AS study_start,
dbo.Optagelse_Studiestatus.AFGANGSARSAG AS Code,
dbo.Optagelse_Studiestatus.KORT_BETEGNELSE AS Expl,
ISNULL((CAST(dbo.Optagelse_Studiestatus.Studiestatus AS varchar(20))), 'Indskrevet') AS 'Desc',
dbo.STUDIESTARTER.OPTAG_START_MANED AS Startmonth,
dbo.ANSOGNINGER.ANSOG_ID as App_id,
dbo.ANSOGNINGER.ANKOMSTDATO AS Data_arrival',
dbo.ANSOGNINGER.EFTEROPTAG AS Efter_op,
dbo.ANSOGNINGER.STATUSDATO AS Date_begin
FROM dbo.INSTITUTIONER
INNER JOIN dbo.PopulationStam_V
ON dbo.INSTITUTIONER.INST_ID = dbo.PopulationStam_V.SEMI_ID
LEFT JOIN dbo.ANSOGNINGER
ON dbo.PopulationStam_V.ELEV_ID = dbo.ANSOGNINGER.ELEV_ID
INNER JOIN dbo.STUDIESTARTER
ON dbo.PopulationStam_V.STUDST_ID_OPRINDELIG = dbo.STUDIESTARTER.STUDST_ID
INNER JOIN dbo.UDD_NAVNE_T
ON dbo.PopulationStam_V.UDDA_ID = dbo.UDD_NAVNE_T.UDD_ID
INNER JOIN dbo.UDDANNELSER
ON dbo.UDD_NAVNE_T.UDD_ID = dbo.UDDANNELSER.UDDA_ID
LEFT OUTER JOIN dbo.PERSONER
ON dbo.PopulationStam_V.PERS_ID = dbo.PERSONER.PERS_ID
LEFT OUTER JOIN dbo.POSTNR
ON dbo.PERSONER.PONR_ID = dbo.POSTNR.PONR_ID
LEFT OUTER JOIN dbo.KønAlleElevID_V
ON dbo.PopulationStam_V.ELEV_ID = dbo.KønAlleElevID_V.ELEV_ID
LEFT OUTER JOIN dbo.Optagelse_Studiestatus
ON dbo.PopulationStam_V.AFAR_ID = dbo.Optagelse_Studiestatus.AFAR_ID
LEFT OUTER JOIN dbo.frafaldsmodel_adgangsgrundlag
ON dbo.frafaldsmodel_adgangsgrundlag.ELEV_ID = dbo.PopulationStam_V.ELEV_ID
LEFT OUTER JOIN dbo.Optagelse_prioriteterUFM
ON dbo.Optagelse_prioriteterUFM.cpr = dbo.PopulationStam_V.CPR_NR
AND dbo.Optagelse_prioriteterUFM.Aar = dbo.frafaldsmodel_adgangsgrundlag.optagelsesaar
LEFT OUTER JOIN dbo.frafaldsmodel_stoettetabel_uddannelser AS fsu
ON fsu.id_uddannelse = dbo.UDDANNELSER.UDDA_ID
AND fsu.id_inst = dbo.INSTITUTIONER.INST_ID
AND fsu.uddannelse_aar = dbo.frafaldsmodel_adgangsgrundlag.optagelsesaar
WHERE dbo.STUDIESTARTER.STUDIESTARTSDATO > '2012-03-01 00:00:00.000'
AND (dbo.Optagelse_Studiestatus.AFGANGSARSAG IS NULL
OR dbo.Optagelse_Studiestatus.AFGANGSARSAG NOT LIKE '2.7.4')
AND (dbo.PopulationStam_V.INDSKRIVNINGSFORM = '1100'
OR dbo.PopulationStam_V.INDSKRIVNINGSFORM = '1700')
GROUP BY dbo.PopulationStam_V.ELEV_ID,
dbo.PopulationStam_V.PERS_ID,
dbo.STUDIESTARTER.STUDST_ID,
dbo.Optagelse_Studiestatus.AFGANGSARSAG,
dbo.Optagelse_Studiestatus.KORT_BETEGNELSE,
dbo.STUDIESTARTER.OPTAG_START_MANED,
Studiestatus,
dbo.ANSOGNINGER.ANSOG_ID,
dbo.ANSOGNINGER.ANKOMSTDATO,
dbo.ANSOGNINGER.EFTEROPTAG,
dbo.ANSOGNINGER.STATUSDATO
I really hope somebody out there can help.

Answer 1

Many ways, this will work:
WITH subSource AS (
/* Your query here */
)
SELECT
s1.id,
/* all other columns work like this:
COALESCE(S1.column,s2.column)
for example: */
coalesce(s1.appid,s2.appid) as appid
FROM subSource s1
INNER JOIN subSource s2
ON s1.study_id =s2.study_id
and s1.study_start = s2.study_start
AND s1.id > s2.id
/* I imagine some other clauses might be needed but maybe not */
The rest is copy paste