CODEWITHSUNDEEP
sqlsql-servert-sqlsql-server-2012
Jeff
Jeff

Reputation: 36573

TSQL OR Query Plan Hints

What kind of query hints can I use to improve the performance of an OR query.

Individually the two queries below run instantly and return 0 rows.

SELECT * FROM AuditInfo ai
WHERE (ai.AppointmentIdForChange = 60231)
and ai.objectname = 'dbo.Appointments'

SELECT * FROM AuditInfo ai
WHERE (ai.AppointmentIdForKey = 60231)
and ai.objectname = 'dbo.Appointments'

AuditInfo is a view.

However the following query runs forever (10+ minutes)

SELECT * FROM AuditInfo ai
WHERE (ai.AppointmentIdForKey= 60231 OR ai.AppointmentIdForChange = 60231)
and ai.objectname = 'dbo.Appointments'

How can I improve this? Are there query hints I can use?

In the estimated execution plan, I can see the individual queries use Key Lookups, whereas the query with the OR statement uses Index Seeks (which takes 74% of the cost).

UPDATE:

The AuditInfo view is defined as follows:

ALTER VIEW AuditInfo
AS
SELECT 
    ae.Id
    ,ae.AuditDateTime AS DateTime
    ,ae.ChangeTypeId
    ,ae.ObjectName
    ,aek.KeyName
    ,aek.KeyValue
    ,aek.KeyValueNumeric
    ,ae.UserId
    ,ae.HostName
    ,ae.ServerName
    ,aec.OldValue   
    ,(SELECT TOP 1 aecNewValue.OldValue AS Value
        FROM dbo.AuditEntries aeNewValue
        JOIN dbo.AuditEntryKeyValues aekNewValue ON aeNewValue.Id = aekNewValue.AuditEntryId AND aek.KeyName = aekNewValue.KeyName AND aek.KeyValueNumeric = aekNewValue.KeyValueNumeric
        JOIN dbo.AuditEntryChanges aecNewValue ON aeNewValue.Id = aecNewValue.AuditEntryId AND aec.ColumnName = aecNewValue.ColumnName
        WHERE aeNewValue.ChangeTypeId IN (0, 1) AND aeNewValue.AuditDateTime > ae.AuditDateTime AND aeNewValue.ObjectName = ae.ObjectName
        ORDER BY aeNewValue.AuditDateTime 
    ) AS NewValue
    ,appointmentForKey.AppointmentId AS AppointmentIdForKey, appointmentForChange.AppointmentId AS AppointmentIdForChange
FROM dbo.AuditEntries ae
JOIN dbo.AuditEntryKeyValues aek on ae.Id = aek.AuditEntryId
LEFT JOIN dbo.AuditEntryChanges aec on ae.Id = aec.AuditEntryId AND aec.ColumnName IN ('PatientId', 'AppointmentId')

-- Get AppointmentId
LEFT JOIN dbo.Appointments appointmentForKey ON aek.KeyName = 'AppointmentId' AND aek.KeyValueNumeric = appointmentForKey.AppointmentId
LEFT JOIN dbo.Appointments appointmentForChange ON aec.ColumnName = 'AppointmentId' AND aec.OldValueNumeric = appointmentForChange.AppointmentId

GROUP BY ae.Id, ae.AuditDateTime, ae.UserId, ae.ChangeTypeId, ae.ObjectName, ae.HostName, ae.ServerName, aek.KeyName, aek.KeyValue, aek.KeyValueNumeric, aec.OldValueNumeric, aec.OldValue, aec.ColumnName
,appointmentForKey.AppointmentId, appointmentForChange.AppointmentId

Upvotes: 2

Views: 323

Answers (1)

paparazzo
paparazzo

Reputation: 45096

I know you ask for query hints but you could just run it as two queries with a union 

SELECT * FROM AuditInfo ai
WHERE (ai.AppointmentIdForChange = 60231)
and ai.objectname = 'dbo.Appointments'
UNION
SELECT * FROM AuditInfo ai
WHERE (ai.AppointmentIdForKey = 60231)
and ai.objectname = 'dbo.Appointments'

As for will it perform tomorrow.
I will take a UNION over a JOIN or an OR for stability.
With a Union SQL does them one at a time and the query optimizer has less chance of getting stupid.

Upvotes: 1

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