How to increase performance of this query? - sql-server

Question

I have an SQL query, it is running on MSSQL 2008 R2
View vMobileLastMobileHistory has about 1000 rows and
select * from vMobileLastMobileHistory is taking 0.2 sec
but this query is taking 5 seconds, how can I optimize this code?
(I think the problem is INTERSECT but I dont know how change this)
SELECT DISTINCT *
FROM
(
SELECT vMobileLastMobileHistory.*
FROM vMobileLastMobileHistory
LEFT OUTER JOIN MobileType_DomainAction ON
MobileType_DomainAction.tiMobileType = vMobileLastMobileHistory.tiMobileType
LEFT OUTER JOIN MobileType_User ON
MobileType_User.MobileID = MobileType_DomainAction.ID
WHERE MobileType_User.UserID = #UserID OR #UserID = - 1
INTERSECT
SELECT vMobileLastMobileHistory.*
FROM vMobileLastMobileHistory
LEFT OUTER JOIN dbo.Region_User ON
dbo.vMobileLastMobileHistory.strRegion = dbo.Region_User.strRegion
WHERE Region_User.iSystemUser = #UserID OR #UserID = - 1
INTERSECT
SELECT vMobileLastMobileHistory.*
FROM vMobileLastMobileHistory
LEFT OUTER JOIN Contractor_User ON
vMobileLastMobileHistory.strContractor = Contractor_User.strContractor
WHERE Contractor_User.iSystemUser = #UserID OR #UserID = - 1
)

Answer 1

The problem is that if you have any indexes on your iSytemUser columns, the optimise is unable to use them because it has to account for a specific userID being passed, or returning all results, it would be better to logically separate your two cases. In addition, since you don't care about any columns in the auxiliary tables, you could use EXISTS in your case of specific users to take advantage of a semi join:
IF (#UserID = -1)
BEGIN
SELECT DISTINCT *
FROM vMobileLastMobileHistory;
END
ELSE
BEGIN
SELECT DISTINCT *
FROM vMobileLastMobileHistory AS mh
WHERE EXISTS
( SELECT 1
FROM Contractor_User AS cu
WHERE cu.strContractor = mh.strContractor
AND cu.iSystemUser = #UserID
)
AND EXISTS
( SELECT 1
FROM Region_User AS ru
WHERE ru.strRegion = mh.strRegion
AND ru.iSystemUser = #UserID
)
AND EXISTS
( SELECT 1
FROM MobileType_DomainAction AS da
INNER JOIN MobileType_User AS mu
ON mu.MobileID = da.ID
WHERE da.tiMobileType = mh.tiMobileType
AND mu.iSystemUser = #UserID
);
END
Now you can have two execution plans for each case (returning all results, or for a specific user), in each case you only need to read from vMobileLastMobileHistory once, and you also limit the sorts required by removing the INTERSECT and replacing with 3 EXISTS clauses.
If they don't already exist then you may also which to consider some indexes on your tables. A good way of finding out what indexes would help is to run the query in SQL Server Management Studio with the option "Show Actual Execution Plan" enabled, this will then show you any missing indexes.

Answer 2

Most of time Intersect and Inner Join will be same. You are not share your data, so based on my knowledge and this link, I just replace intersect query into Inner join query as :
--I think you don't need distinct upper query. If you have issue inform me.
SELECT DISTINCT vml.*
FROM vMobileLastMobileHistory vml
LEFT OUTER JOIN MobileType_DomainAction mtda ON mtda.tiMobileType = vml.tiMobileType
LEFT OUTER JOIN MobileType_User ON MobileType_User.MobileID = mtda.ID
LEFT OUTER JOIN dbo.Region_User ON dbo.vml.strRegion = dbo.Region_User.strRegion
LEFT OUTER JOIN Contractor_User ON vml.strContractor = Contractor_User.strContractor
WHERE
(MobileType_User.UserID = #UserID
and Region_User.iSystemUser = #UserID or Contractor_User.iSystemUser = #UserID
) OR #UserID = - 1