Question

I’m trying to write a lookup method for determining a SMS message to send to a user based on a few parameters associated with the user/system. We will have a default message that will be used as a last resort, but there are multiple ways to override the message by various parameters. Here is what I have so far for the lookup query – are there any better ways to do this? Maybe a lookup is not the right approach for this?

Here is the lookup table:

MessageLookup { ID bigint PK                           Key varchar                            CampaignTypeID bigint FK,              ServiceProviderID bigint FK nullable, -- optional override parameter DistributorID bigint FK nullable,     -- optional override parameter CampaignID bigint FK nullable,        -- optional override parameter Message varchar                    } 

Here is an example of what the table would look like:

   ID Key  CTID SPID DistID CampID Message     1 Help 1    NULL NULL   NULL   'This is the default message'     2 Help 1    375  NULL   NULL   'This is the SP375 message'     3 Help 1    377  NULL   NULL   'This is the SP377 message'     4 Help 1    NULL 13     NULL   'This is the Dist13 message'     5 Help 1    375  13     NULL   'This is the SP375/Dist13 message'     6 Help 1    NULL 13     500    'This is the Dist13/Camp500 message'     7 Help 1    375  13     500    'This is the SP375/Dist13/Camp500 msg'     8 Help 1    NULL NULL   500    'This is the Camp500 help message' 

Here is the query I have:

select     --top 1     * from MessageLookup ml where ml.[Key] = @Key and ml.CampaignTypeID = @CampaignTypeID and (     ml.ServiceProviderID = @ServiceProviderID or     ml.ServiceProviderID is null ) and (     ml.DistributorID = @DistributorID or     ml.DistributorID is null ) and (     ml.CampaignID = @CampaignID or     ml.CampaignID is null ) order by     CampaignID desc, -- highest precedence lookup param     DistributorID desc,     ServiceProviderID desc -- lowest precedence lookup param 

Answer 1

I’m not sure what the best way is, but here are some alternatives:

One thought would be to store a pattern with each rule, like so:

ID Key CTID Rule        Message 1 Help 1    '[%:%:%]'    'This is the default message' 2 Help 1    '[375:%:%]'  'This is the SP375 message' 3 Help 1    '[377:%:%]'  'This is the SP377 message' 4 Help 1    '[%:13:%]'   'This is the Dist13 message' 5 Help 1    '[375:13:%]' 'This is the SP375/Dist13 message' 

and then use a LIKE test instead of all the ANDs.

Another thought would be to use OUTER JOINS.

Or (playing off the answer that just came in) to DRY things up further by writing:

where ml.[Key] = @Key   and ml.CampaignTypeID = @CampaignTypeID   and IsNull(ml.ServiceProviderID = @ServiceProviderID,true)   and IsNull(ml.DistributorID     = @DistributorID,    true)   and IsNull(ml.CampaignID        = @CampaignID,       true)