Show unique value for id, based on latest createby date - sql

Question

I am using the following SQL code to JOIN a few tables, but need to show unique values for the s.incidentid based on the latest s.createdate.
I know I need to use a Sub query with Maxdate, but I am not sure on the correct syntax.
This is my first query with multiple joins and I am struggling to get my head round it.
Here is my code:
SELECT
s.incidentid,
u.internalid as AssignedTo,
u.fullname as AssignedTo_FullName,
s.createby as AssignedBy,
u2.fullname as AssignedBy_FullName,
s.createdate as AssignedTime,
i.[description],
i.fix,
st.[description] as [Status],
(SELECT (CASE WHEN u.internalid = s.createby THEN 'Yes' ELSE 'No' END) as SelfAssigned),
d.d1,
d.d2,
d.d3,
d.d4,
d.d5
FROM dbo.IncidentServiceLevelAgreement s
JOIN dbo.UserAll u on u.userid = s.userid
JOIN dbo.UserAll u2 on u2.internalid = s.createby
JOIN dbo.IncidentAll i on s.incidentid = i.incidentid
JOIN dbo.[Status] st on i.statusid = st.statusid
JOIN dbo.flatdiagnosis d on i.actualdiagnosisid = d.diagnosisid
WHERE (s.groupId = '4954' and s.incidentServiceLevelAgreementTypeID = '9')
ORDER BY AssignedTime DESC
Any help greatly appreciated.

Answer 1

The easiest is to use a CTE and the ROW_NUMBER function:
WITH CTE AS
(
SELECT RN = ROW_NUMBER() OVER ( PARTITION BY incidentid
ORDER BY createdate DESC ),
s.Incidentid,
u.Internalid AS AssignedTo,
u.Fullname AS AssignedTo_FullName,
s.Createby AS AssignedBy,
u2.Fullname AS AssignedBy_FullName,
s.Createdate AS AssignedTime,
i.[Description],
i.Fix,
st.[Description] AS [Status],
SelfAssigned = CASE WHEN u.Internalid = s.Createby
THEN 'Yes' ELSE 'No' END,
d.D1,
d.D2,
d.D3,
d.D4,
d.D5
FROM dbo.Incidentservicelevelagreement s
JOIN dbo.Userall u
ON u.Userid = s.Userid
JOIN dbo.Userall u2
ON u2.Internalid = s.Createby
JOIN dbo.Incidentall i
ON s.Incidentid = i.Incidentid
JOIN dbo.[Status] st
ON i.Statusid = st.Statusid
JOIN dbo.Flatdiagnosis d
ON i.Actualdiagnosisid = d.Diagnosisid
WHERE ( s.Groupid = '4954'
AND s.Incidentservicelevelagreementtypeid = '9' )
)
SELECT * FROM CTE WHERE RN = 1
ORDER BY AssignedTime DESC
(instead of SELECT * list all columns explicitly, I didn't feel like it)