SQL: SELECT by priority

nospam@example.com (Sune Trudslev) — Fri, 30 Sep 2005 18:57:00 +0200

I have been working on a project at work where it should be possible to set up what suppliers are available to our customers and their users. We also wanted to be able to be able to provide the customers with a standard setup (sort of a template) based on what type of product they are using.

Here is the solution I came up with.

First the tables we already have available:

Customer

Column Name	Value
CustomerId	Int (PK)
CustomerName	Varchar(30)

Office

Column Name	Value
OfficeId	Int (PK)
CustomerId	Int (FK)
SupplierTemplateId	Int (FK)
OfficeName	Varchar(30)

Supplier

Column Name	Value
SupplierId	Int (PK)
SupplierName	Varchar(30)

So then we will need to add a table to hold the templates:

SupplierTemplate

Column Name	Value
SupplierTemplateId	Int (PK)
SupplierTemplateName	Varchar(30)

Last but not least we will need a table to hold the actual supplier selection:

SupplierSetting

Column Name	Value
SupplierSettingId	Int (PK)
SupplierId	Int (FK)
SupplierTemplateId	Int (FK) NULL
CustomerId	Int (FK) NULL
OfficeId	Int (FK) NULL
Enabled	Bit
Priority	Int

A setting can either belong to a template, a customer, a registration number or none (which makes it a default setting).

The priority is assigned as follows:

Condition	Priority
No owner	1
Owned by a template	2
Owned by a customer	3
Owned by a registration	4

So now we can fill in some data:

Customer

CustomerId	CustomerName
1	Test Customer

SupplierTemplate

SupplierTemplateId	SupplierTemplateName
1	Template 1

Office

OfficeId	CustomerId	SupplierTemplateId	OfficeName
1	1	1	Test Office

Supplier

SupplierId	SupplierName
1	Test Supplier 1
2	Test Supplier 2

Now all that is left is set up the suppliers:

SupplierSetting

SupplierSettingId	SupplierId	SupplierTemplateId	CustomerId	OfficeId	Enabled	Priority
1	1	NULL	NULL	NULL	true	1
2	2	NULL	NULL	NULL	false	1
3	2	1	NULL	NULL	true	2
4	1	NULL	1	NULL	false	3

Here is a textual representation of the above data:

On a global (default) level 'Test Supplier 1' is turned on and 'Test Supplier 2' is turned off.
On 'Test Customer' level 'Test Supplier 2' is turned on'
On 'Test Office' level 'Test Supplier 1' is turned off.

So how do we get this data out so we only have one row per supplier with the correct status? Well, the answer is a SELECT statement with a sub-SELECT to find the highest priority for the current supplier. Enjoy!

Here it is:

DECLARE @OfficeId INT
SELECT @OfficeId = 1

DECLARE @CustomerId INT
DECLARE @SupplierTemplateId INT
SELECT
  @CustomerId = CustomerId,
  @SupplierTemplateId = SupplierTemplateId 
FROM 
  Office 
WHERE 
  OfficeId = @OfficeId

SELECT 
  * 
FROM 
  SupplierSetting s1 
WHERE 
  (CustomerId  = @CustomerId OR CustomerId IS NULL) AND
  (SupplierTemplateId = @SupplierTemplateId OR SupplierTemplateId IS NULL) AND
  (OfficeId = @OfficeId OR OfficeId IS NULL) AND
  Priority = (
    SELECT 
      MAX(Priority) 
    FROM 
      SupplierSetting s2 
    WHERE 
      s1.SupplierId = s2.SupplierId AND
      (CustomerId  = @CustomerId OR CustomerId IS NULL) AND
      (SupplierTemplateId = @SupplierTemplateId OR SupplierTemplateId IS NULL) AND
      (OfficeId = @OfficeId OR OfficeId IS NULL)
  )

Sune Trudslev's WebLog - SQL

SQL: SELECT by priority