One Active Record per ID - sql-server-2012

Question

The address table is shared for both companies and contacts. I have a constraint that prevents the user from adding a record with both a Company ID and a Contact ID. I am trying to add another constraint to have only 1 active (ACTIVE FLAG = 'TRUE') address per Company ID or Contact ID. But I want to be able to have unlimited inactive (ACTIVE FLAG = 'FALSE').
ALTER TABLE [dbo].[ADDRESSES] WITH CHECK ADD CONSTRAINT [chk_ONLY_ONE_ACTIVE_ADDRESS] CHECK (([COMPANY_ID] IS NOT NULL AND [CONTACT_ID] IS NULL AND [ACTIVE] = 'TRUE' OR [COMPANY_ID] IS NULL AND [CONTACT_ID] IS NOT NULL AND [ACTIVE] = 'TRUE' OR [COMPANY_ID] IS NULL AND [CONTACT_ID] IS NOT NULL AND [ACTIVE] = 'FALSE' OR [COMPANY_ID] IS NOT NULL AND [CONTACT_ID] IS NULL AND [ACTIVE] = 'FALSE'))
GO
Where am I missing it?
Thanks
jlimited

Answer 1

You are adding the constraint 'active=true' and 'active=false' for both combinations of contact id and company id so it's a tautology, you may as well remove this constraint.
I believe the only way to enforce the rule 'only one active flag and 0 to many inactive' is by triggers.

Answer 2

Thanks for the reply Jayvee. Here is the solution that I figured out.
I first created two functions...
One
CREATE FUNCTION [dbo].[fnCheckForActiveContactAddress](
#id int
)
RETURNS INT
AS
BEGIN
DECLARE #result INT
IF #id IS NOT NULL
SET #result = ISNULL((select count(*) from dbo.Addresses where CONTACT_ID = #ID AND ACTIVE = 'TRUE'),0)
ELSE
SET #result = 1
RETURN #result
END
GO
Two
CREATE FUNCTION [dbo].[fnCheckForActiveCompanyAddress](
#id int
)
RETURNS INT
AS
BEGIN
DECLARE #result INT
If #id IS NOT NULL
SET #result = ISNULL((select count(*) from dbo.Addresses where COMPANY_ID = #ID AND ACTIVE = 'TRUE'),0)
ELSE
SET #result = 1
RETURN #result
END
GO
Then I added the following constraints...
ALTER TABLE [dbo].[ADDRESSES] WITH CHECK ADD CONSTRAINT [chk_COMPANY_OR_CONTACT] CHECK (([COMPANY_ID] IS NOT NULL AND [CONTACT_ID] IS NULL OR [COMPANY_ID] IS NULL AND [CONTACT_ID] IS NOT NULL))
GO
ALTER TABLE [dbo].[ADDRESSES] WITH NOCHECK ADD CONSTRAINT [CHK_ADDRESSES_ONLY_ONE_ACTIVE_CONTACT] CHECK (([dbo].[fnCheckForActiveContactAddress]([CONTACT_ID])=(1)))
GO
ALTER TABLE [dbo].[ADDRESSES] WITH NOCHECK ADD CONSTRAINT [CHK_ADDRESSES_ONLY_ONE_ACTIVE_COMPANY] CHECK (([dbo].[fnCheckForActiveCompanyAddress]([COMPANY_ID])=(1)))
GO
This solution seems to work well.
Any thoughts on improving it?
jlimited

Answer 3

If I understand your requirements, this should work (if -1 is not a valid CompanyID or ContactID):
create table T (
CompanyID int,
ContactID int,
BothIDs as
CASE WHEN CompanyID IS NOT NULL and ContactID IS NOT NULL
THEN 1 ELSE 0 END PERSISTED
check (BothIDs = 0),
ActiveFlag varchar(5) check (ActiveFlag in ('TRUE','FALSE')),
ActiveCheck as
CASE WHEN ActiveFlag='TRUE' then -1 ELSE COALESCE(CompanyID,ContactID) END,
unique (ActiveCheck)
);
insert into T values
(1,NULL,'FALSE'),
(NULL,2,'FALSE'),
(3,NULL,'TRUE'),
(4,NULL,'FALSE');
GO
UPDATE T SET
ActiveFlag = 'TRUE'
WHERE CompanyID = 4;