How to handle an empty result set from an OpenQuery call to linked analysis server in dynamic SQL? - tsql

Question

I have a number of stored procedures structured similarly to this:
DECLARE #sql NVARCHAR(MAX)
DECLARE #mdx NVARCHAR(MAX)
CREATE table #result
(
[col1] NVARCHAR(50),
[col2] INT,
[col3] INT
)
SET #mdx = '{some dynamic MDX}'
SET #sql = 'SELECT a.* FROM OpenQuery(LinkedAnalysisServer, ''' + #mdx + ''') AS a'
INSERT INTO #result
EXEC sp_executesql #sql
SELECT * FROM #result
This works quite well when results exist in the cube. However, when the OpenQuery results are empty, the INSERT fails with this error:
Column name or number of supplied
values does not match table
definition.
My question is, what is the best way to handle this scenario? I'm using the results in a static report file (.rdlc), so the explicit typing of the temp table is (I'm pretty sure) required.

Answer 1

Use TRY/CATCH in your stored procedure, you'll notice there is a specific error number for your problem, so check the error number and if it is that, return an empty result set. As you already have the table defined that'll be easier.
PseudoCode looks something like this:
SET #mdx = '{some dynamic MDX}'
SET #sql = 'SELECT a.* FROM OpenQuery(LinkedAnalysisServer, ''' + #mdx + ''') AS a'
BEGIN TRY
INSERT INTO #result
EXEC sp_executesql #sql
END TRY
BEGIN CATCH
IF ERROR_NUMBER <> 'The error number you are seeing'
BEGIN
RAISERROR('Something happened that was not an empty result set')
END
END CATCH
SELECT * FROM #result
You'll want to check for that particular error, so that you don't just return empty result sets if your SSAS server crashes for example.

Answer 2

There is another solution to this issue, similar to the accepted answer, which involves using an IF statement instead of TRY...CATCH.
http://www.triballabs.net/2011/11/overcoming-openquery-mdx-challenges/
IF (SELECT COUNT(*)
FROM OPENQUERY("SSAS1",
'SELECT [Measures].[Target Places] ON COLUMNS
FROM [ebs4BI_FactEnrolment]
WHERE [DimFundingYear].[Funding Year].&[17]')) > 0
EXEC sp_executesql N'SELECT CONVERT(varchar(20),
"[DimPAPSCourse].[Prog Area].[Prog Area].[MEMBER_CAPTION]")
as ProgArea,
convert(float, "[Measures].[Target Places]") as Target
FROM OPENQUERY("SSAS1",
''SELECT [Measures].[Target Places] ON COLUMNS,
[DimPAPSCourse].[Prog Area].[Prog Area] ON ROWS
FROM [ebs4BI_FactEnrolment]
WHERE [DimFundingYear].[Funding Year].&[17]'')'
ELSE
SELECT '' as ProgArea, 0 as Target
WHERE 1=0