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Why does this SQL result in indexing instead of index?

Can someone help me customize this SQL query?

SELECT  a.BuildingID, a.ApplicantID, a.ACH, a.Address, a.Age, a.AgentID, a.AmenityFee, a.ApartmentID, a.Applied, a.AptStatus, a.BikeLocation, a.BikeRent, a.Children, 
        a.CurrentResidence, a.Email, a.Employer, a.FamilyStatus, a.HCMembers, a.HCPayment, a.Income, a.Industry, a.Name, a.OccupancyTimeframe, a.OnSiteID,
        a.Other, a.ParkingFee, a.Pets, a.PetFee, a.Phone, a.Source, a.StorageLocation, a.StorageRent, a.TenantSigned, a.WasherDryer, a.WasherRent, a.WorkLocation, 
        a.WorkPhone, a.CreationDate, a.CreatedBy, a.LastUpdated, a.UpdatedBy
FROM    dbo.NPapplicants AS a INNER JOIN
        dbo.NPapartments AS apt ON a.BuildingID = apt.BuildingID AND a.ApartmentID = apt.ApartmentID
WHERE   (apt.Offline = 0)
AND     (apt.MA = 'M')

.

The execution plan looks like this:

.

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I do not understand why I get index scans for NPapplicants. I have an Index that contains BuildingID and ApartmentID. Should this not be used?

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2 answers

This is because he will return from matches closer to 10K records. Returning to data to retrieve other columns using 10K keys is equivalent to what works only when scanning 100 thousand records (at least) and filtering using hash match.

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SET STATISTICS IO ON
SET STATSTICS TIME ON

SELECT  a.BuildingID, a.ApplicantID, a.ACH, a.Address, a.Age, a.AgentID, a.AmenityFee, a.ApartmentID, a.Applied, a.AptStatus, a.BikeLocation, a.BikeRent, a.Children, 
        a.CurrentResidence, a.Email, a.Employer, a.FamilyStatus, a.HCMembers, a.HCPayment, a.Income, a.Industry, a.Name, a.OccupancyTimeframe, a.OnSiteID,
        a.Other, a.ParkingFee, a.Pets, a.PetFee, a.Phone, a.Source, a.StorageLocation, a.StorageRent, a.TenantSigned, a.WasherDryer, a.WasherRent, a.WorkLocation, 
        a.WorkPhone, a.CreationDate, a.CreatedBy, a.LastUpdated, a.UpdatedBy
FROM    dbo.NPapplicants AS a INNER JOIN
        dbo.NPapartments AS apt ON a.BuildingID = apt.BuildingID AND a.ApartmentID = apt.ApartmentID
WHERE   (apt.Offline = 0)
AND     (apt.MA = 'M')

SELECT  a.BuildingID, a.ApplicantID, a.ACH, a.Address, a.Age, a.AgentID, a.AmenityFee, a.ApartmentID, a.Applied, a.AptStatus, a.BikeLocation, a.BikeRent, a.Children, 
        a.CurrentResidence, a.Email, a.Employer, a.FamilyStatus, a.HCMembers, a.HCPayment, a.Income, a.Industry, a.Name, a.OccupancyTimeframe, a.OnSiteID,
        a.Other, a.ParkingFee, a.Pets, a.PetFee, a.Phone, a.Source, a.StorageLocation, a.StorageRent, a.TenantSigned, a.WasherDryer, a.WasherRent, a.WorkLocation, 
        a.WorkPhone, a.CreationDate, a.CreatedBy, a.LastUpdated, a.UpdatedBy
FROM    dbo.NPapplicants WITH (INDEX (index_name)) AS a
INNER JOIN
        dbo.NPapartments AS apt ON a.BuildingID = apt.BuildingID AND a.ApartmentID = apt.ApartmentID
WHERE   (apt.Offline = 0)
AND     (apt.MA = 'M')

index_name I/O ( )

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