Call SQL Functions after PIVOT - sql

Question

I have a stored procedure that's taking a very long time because I have 2 function calls that are being called before a PIVOT, which means it's calling the functions 5 times for each record rather than once for each record. How can I get rewrite my query so that the 2 function calls right at the end of the query are run after the Pivot rather than before?
Here's the query
CREATE TABLE #Temp
(
ServiceRecordID INT,
LocationStd VARCHAR(1000),
AreaServedStd VARCHAR(1000),
RegionalLimited BIT,
Region VARCHAR(255),
Visible BIT
)
DECLARE #RegionCount INT
SELECT #RegionCount = COUNT(RegionID) FROM Regions WHERE SiteID = #SiteID AND RegionID % 100 != 0
INSERT INTO #Temp
SELECT TOP (#RegionCount * 100) SR.ServiceRecordID, SR.LocationStd, SR.AreaServedStd, SR.RegionalLimited, R.Region,
CASE WHEN (ISNULL(R_SR.RegionID,0) = 0 AND ISNULL(R_SR_Serv.RegionID,0) = 0) THEN 0 ELSE 1 END AS Visible
FROM ServiceRecord SR
INNER JOIN Sites S ON SR.SiteID = S.SiteID
INNER JOIN Regions R ON R.SiteID = S.SiteID
LEFT OUTER JOIN lkup_Region_ServiceRecord R_SR ON R_SR.RegionID = R.RegionID AND R_SR.ServiceRecordID = SR.ServiceRecordID
LEFT OUTER JOIN lkup_Region_ServiceRecord_Serv R_SR_Serv ON R_SR_Serv.RegionID = R.RegionID AND R_SR_Serv.ServiceRecordID = SR.ServiceRecordID AND SR.RegionalLimited = 0
WHERE SR.SiteID = #SiteID
AND R.RegionID % 100 != 0
ORDER BY SR.ServiceRecordID
DECLARE #RegionList varchar(2000),#SQL varchar(max)
SELECT #RegionList = STUFF((SELECT DISTINCT ',[' + Region + ']' FROM #Temp ORDER BY ',[' + Region + ']' FOR XML PATH('')),1,1,'')
SET #SQL='SELECT * FROM
(SELECT ServiceRecordID,
dbo.fn_ServiceRecordGetServiceName(ServiceRecordID,'''') AS ServiceName,
LocationStd,
AreaServedStd,
RegionalLimited,
Region As Region,
dbo.fn_GetOtherRegionalSitesForServiceRecord(ServiceRecordID) AS OtherSites,
CAST(Visible AS INT) AS Visible FROM #Temp) B PIVOT(MAX(Visible) FOR Region IN (' + #RegionList + ')) A'
EXEC(#SQL)

Answer 1

Move the function calls after the PIVOT:
SET #SQL='
SELECT
A.*,
N.ServiceName,
S.OtherSites
FROM
(
SELECT
ServiceRecordID,
LocationStd,
AreaServedStd,
RegionalLimited,
Region,
CAST(Visible AS INT) AS Visible
FROM #Temp
) B
PIVOT(MAX(Visible) FOR Region IN (' + #RegionList + ')) A
OUTER APPLY (
SELECT dbo.fn_ServiceRecordGetServiceName(A.ServiceRecordID,'''')
) N (ServiceName)
OUTER APPLY (
SELECT dbo.fn_GetOtherRegionalSitesForServiceRecord(A.ServiceRecordID)
) S (OtherSites);
';
Or just put them in the outer SELECT:
SET #SQL='
SELECT
A.*,
ServiceName = dbo.fn_ServiceRecordGetServiceName(A.ServiceRecordID,''''),
OtherSites = dbo.fn_GetOtherRegionalSitesForServiceRecord(A.ServiceRecordID)
FROM
(
SELECT
ServiceRecordID,
LocationStd,
AreaServedStd,
RegionalLimited,
Region,
CAST(Visible AS INT) AS Visible
FROM #Temp
) B
PIVOT(MAX(Visible) FOR Region IN (' + #RegionList + ')) A
';
If you can possibly convert those functions to be table-valued rowset-returning consisting of a single SELECT statement, you may get a huge performance improvement as well.
CREATE FUNCTION dbo.fn_ServiceRecordGetServiceName2(
#ServiceRecordID itn
)
RETURNS TABLE
AS
RETURN ( -- single select statement
SELECT ServiceName = Blah
FROM dbo.Gorp
WHERE Gunk = 'Ralph'
);
Then
OUTER APPLY dbo.fn_ServiceRecordGetServiceName(ServiceRecordID,'''') N
And N.ServiceName will return the value(s).
Also, it is not correct to tack on square brackets to convert data values to valid sysnames. You should use the QuoteName function. This will ensure your system doesn't break no matter WHAT crazy value is entered 13 years from now (think 'Taiwan [North]'):
STUFF((SELECT DISTINCT ',' + QuoteName(Region) FROM #Temp ...
Note:
Since you said that this is for display in a web page, you don't even need to do the pivoting on the server. Instead, return 2 rowsets to the client, one with the Site data and one with the column data for the Regions. You would need an additional pass through every row in the Region rowset to find out all the regions needed, but this can be done very quickly. Finally, adjust your program code to step through the Region rows as needed for each matching Site, and created your output.
One reason this is worth the investment is that if your application grows in size, you can always throw another web server at the problem, but it's a lot harder to throw another database at it. A new web server will cost less than continually beefing up your SQL Server.
P.S. Even dynamic SQL is easier to deal with when you format it well. :)