How to use “Partition By” or “Max”? for SQL Server - sql

Question

I have a very similar question to what was asked here for an Oracle DB (but I have an SQL Server 2012). The example I have used as a starter is based on the answer given here.
What I have is these four columns:
[L2] ,[DateofReporting],[L3] and [ServerName] more or less at a random day data is added to that table, but if it is, it will always be the same [L2],[DateofReporting],[L3] but with a different [ServerName]
Now I want to extract that data to give me all the servers [ServerName], which were added last for all months and years grouped by L2, L3 and the related month and year (coming from [DateofReporting]) .
SELECT [ID],[L2],[DateofReporting],[L3],[ServerName]
FROM (
select *,
max([DateofReporting])
OVER (PARTITION BY YEAR([DateofReporting]),
Month([DateofReporting])) maxdate
from [EADATAGOV].[Governance].[ToDos]
)max_date
where [DateofReporting] = maxdate
The problem I am phasing is, that the data is incomplete and their is obviously a bug in my statement. By now I don't see the tree for the forest, could you please help me clean up that SQL statement, or if there is a smarter way of doing it, I am open to suggestions.
I was thinking about utilizing ROW_NUMBER() to mark the relevant entries and than do a select on them, but I have never worked with that before.
thx Jan
example of output:
ID L2 DateofReporting L3 name
18214 Summer 2017-09-20 cloud BINHAS01105 <--
18215 Summer 2017-09-20 lightbulb BINHAS60276 <--
18217 Summer 2017-09-20 lightbulb CNAHAS62003 <--
15297 Summer 2017-09-15 cloud CINHAS01105
15298 Summer 2017-09-15 boat CINHAS60277
15300 Summer 2017-09-15 lightbulb DNAHAS62003
10512 Summer 2017-08-20 lightbulb DNAHAS62003 <--
the ones pointed out, are the ones I would expect to see in the result. As eg. boat does not have a newer entry than that of the 09-15.
new approach:
Select [L2],
MAX([DateofReporting]) LDateOfTest
from [EADATAGOV].[Governance].[ToDos]
group by [L2], YEAR([DateofReporting]), Month([DateofReporting]) ,[DType]
having DType= 'test'
order by LDateOfTest desc, L2 desc
This provides me (correctly) the latest date for each L2 for every month. Now in theory I should be able to use another query on the very same table where L2 and the LDateOfTest match.
My idea of a subselect does not work, as I can only pass one criteria, not two. But I don't know how that works, can you help me with the join(?) ?

Answer 1

It's difficult understand your request, since you didn't post any sample data (input).
As far as I understood, may be we can start from this query. Can you try it and pls let me know?
SELECT ID
,L2
,DATEOFREPORTING
,L3
,SERVERNAME
FROM(
SELECT ID
,L2
,DATEOFREPORTING
,L3
,SERVERNAME
,ROW_NUMBER() OVER (PARTITION BY NAME ORDER BY DATEOFREPORTING DESC) RN
FROM TODOS
) A
WHERE RN = 1;

Answer 2

Select [ID],[L2],[DateofReporting],[L3],[ServerName]
From(
Select [ID],[L2],[DateofReporting],[L3],[ServerName],
Row_NUmber() Over(Partition BY [ServerName],[L3] Order BY [DateofReporting] Desc) as Row_Num
from [EADATAGOV].[Governance].[ToDos]
) Temp
Where Row_Num = 1

Answer 3

That's the solution I have come up with after some hours of struggling. I had to completely reset my approach.
IF OBJECT_ID('tempdb..#tmp_table') IS NOT NULL DROP TABLE #tmp_table
Select [L2],
MAX([DateofReporting]) LDateOfTest
into #tmp_table --(L2t, LDateOfTest)
from [EADATAGOV].[Governance].[ToDos]
group by [L2], YEAR([DateofReporting]), Month([DateofReporting]) ,[DType]
having DType = 'test'
order by LDateOfTest desc, L2 desc
SELECT [ID]
,[EADATAGOV].[Governance].[ToDos].[L2] L2f
,YEAR([DateofReporting]) YoT, Month([DateofReporting]) MoT
,[L3]
,[ServerName]
FROM [EADATAGOV].[Governance].[ToDos]
right join #tmp_table tt on tt.L2 = [EADATAGOV].[Governance].[ToDos].[L2] and tt.LDateOfTest = ToDos.DateofReporting
where DType = 'test'
order by DateofReporting desc, L3 asc
DROP TABLE #tmp_table
It probably isn't the prettiest solution, but it get's me the results I was hoping for.