how to omit null values using SQL query - sql

Question

I am trying to only display the rows in which there is date for Researchers.
I cannot manage to omit the rows with Null Values. I even tried this solution How to remove null rows from sql query result?..
This is my Query:
SELECT Submission.Title AS [Submission_Title], CA.Surname AS [Researchers], Submission.Status AS [Status]
FROM Submission
CROSS APPLY (SELECT STUFF((SELECT DISTINCT ', ' + r.Surname
FROM ResearcherSubmission rs INNER JOIN Researcher r
ON r.ResearcherID = rs.ResearcherID
WHERE CONCAT (DATENAME(MONTH,[Submission].[SubmissionDate]), ' ',DATEPART (YEAR,[Submission].[SubmissionDate])) = 'October 2015'
AND Submission.SubmissionID = rs.SubmissionID
FOR XML PATH (''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 2, ' ')) AS CA (Surname)
GROUP BY convert(varchar(10),datename(month,Submission.SubmissionDate)), Submission.Title, CA.Surname, Submission.Status;
This is my Current output:
any suggestion. Thank you

Answer 1

Quickfix, without reading query:
WITH cte AS
(
SELECT Submission.Title AS [Submission_Title], CA.Surname AS [Researchers], Submission.Status AS [Status]
FROM Submission
CROSS APPLY (SELECT STUFF((SELECT DISTINCT ', ' + r.Surname
FROM ResearcherSubmission rs INNER JOIN Researcher r
ON r.ResearcherID = rs.ResearcherID
WHERE CONCAT (DATENAME(MONTH,[Submission].[SubmissionDate]), ' ',DATEPART (YEAR,[Submission].[SubmissionDate])) = 'October 2015'
AND Submission.SubmissionID = rs.SubmissionID
FOR XML PATH (''), TYPE).value('.', 'NVARCHAR(MAX)'), 1, 2, ' ')) AS CA (Surname)
GROUP BY convert(varchar(10),datename(month,Submission.SubmissionDate)), Submission.Title, CA.Surname, Submission.Status
)
SELECT *
FROM cte
WHERE Researchers IS NOT NULL;
There is probably more elegant solution, but you need to share sample data and structures.
This part may cause problems:
SELECT DISTINCT ', ' + r.Surname
try with CONCAT instead or :
SELECT DISTINCT ', ' + ISNULL(r.Surname, '')

Answer 2

You should filter out the researchers before the group by rather than afterwards. When possible, it is better (performance-wise) to put conditions before aggregation.
SELECT s.Title AS Submission_Title, CA.Surname AS Researchers, s.Status
FROM Submission s CROSS APPLY
(SELECT STUFF((SELECT DISTINCT ', ' + r.Surname
FROM ResearcherSubmission rs INNER JOIN
Researcher r
ON r.ResearcherID = rs.ResearcherID
WHERE s.SubmissionID = rs.SubmissionID
FOR XML PATH (''), TYPE).value('.', 'NVARCHAR(MAX)'
), 1, 2, ' '))
) AS CA(Surname)
WHERE s.SubmissionDate >= '2015-10-01' AND s.SubmissionDate < '2015-11-01' AND
ca.Surname IS NULL
GROUP BY YEAR(s.SubmissionDate), MONTH(s.SubmissionDate), s.Title, CA.Surname, s.Status;
Note the changes made:
Table aliases make the query easier to write and to read.
I changed the date comparison to have no functions on the date itself. This would allow SQL Server to use an index, if appropriate.
I also moved the date comparison from the CROSS APPLY subquery to the outer query. This could be a big gain in efficiency. Why do the extra work for rows that will be filtered out anyway?
I added the NOT NULL condition to the WHERE clause.
The date key in the outer GROUP BY is redundant because the query is only using one month of data. I simplified the logic but left it.