Question

Question:

I want to add a unique constraint on a mapping table (n:n).
I want that new values may be inserted, but only if TEST_FK_UID, TEST_DateFrom and TEST_DateTo are not equal to an already existing entry.

The problem is the status field.
Status 1 means active..
Status != 1 means inactive/deleted..
.
.
So one may of course insert a new entry with the same FK, DateFrom and DateTo, IF – and only if – the status of the existing entry (all existing entries, as you can insert, delete, insert, delete, insert, delete, etc.) is != 1

Here is what I have so far:

CREATE TABLE dbo._________Test  
(
     TEST_UID uniqueidentifier NOT NULL 
    ,TEST_FK_UID uniqueidentifier NOT NULL 
    ,TEST_DateFrom DateTime NOT NULL 
    ,TEST_DateTo DateTime NOT NULL  
    ,TEST_Status int NOT NULL 
    ,UNIQUE(TEST_FK_UID, TEST_DateFrom, TEST_DateTo, TEST_Status) 
); 

Answer 1

It is very possible, like this
(basic credit goes to: https://stackoverflow.com/users/103075):

---

Edit:
OK, pedantically seen it’s not a unique constraint, it’s a check constraint, but WTF – it has the same effect and works on SQL-Server 2005 as well, and the (conditional) condition is configurable per customer (replace SET @bNoCheckForThisCustomer = ‘false’ with a select to a configuration table) – that’s not possible with a unique index AFAIK … 😉

---

Note this line:

AND ZO_RMMIO_UID != @in_ZO_RMMIO_UID

(ZO_RMMIO_UID is the unique primary key of the n:n mapping table)

It’s important, since a check constraint seems to be similar to a onAfterInsert trigger.
If this line is missing, it checks on itselfs as well, which leads to the function always returning true…

IF  EXISTS (SELECT * FROM sys.check_constraints WHERE object_id = OBJECT_ID(N'[dbo].[CheckNoDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt]') AND parent_object_id = OBJECT_ID(N'[dbo].[T_ZO_AP_Raum_AP_Ref_Mietobjekt]'))
ALTER TABLE [dbo].[T_ZO_AP_Raum_AP_Ref_Mietobjekt] DROP CONSTRAINT [CheckNoDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt]
GO





IF  EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[fu_InsertCheck_IsDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt]') AND type in (N'FN', N'IF', N'TF', N'FS', N'FT'))
DROP FUNCTION [dbo].[fu_InsertCheck_IsDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt]
GO





-- ========================================================================
-- Author:            Me
-- Create date:       09.08.2010
-- Last modified:     09.08.2010
-- Description:   Conditionally check if row is a duplicate
-- ========================================================================

-- PRE:  UID, Valid RM_UID, Valid MIO_UID, 
--       Valid datetime-from for db usr language, valid datetime-to for db usr language
-- POST: True/False


CREATE  FUNCTION [dbo].[fu_InsertCheck_IsDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt](@in_ZO_RMMIO_UID uniqueidentifier, @in_ZO_RMMIO_RM_UID AS uniqueidentifier, @in_ZO_RMMIO_MIO_UID as uniqueidentifier, @in_ZO_RMMIO_DatumVon AS datetime, @in_ZO_RMMIO_DatumBis AS datetime)
    RETURNS bit
AS
    BEGIN   

        DECLARE @bIsDuplicate AS bit
        SET @bIsDuplicate = 'false'     


        DECLARE @bNoCheckForThisCustomer AS bit
        SET @bNoCheckForThisCustomer = 'false'

        IF @bNoCheckForThisCustomer = 'true'
            RETURN @bIsDuplicate 




        IF EXISTS
        (
            SELECT 
                 ZO_RMMIO_UID
                ,ZO_RMMIO_RM_UID
                ,ZO_RMMIO_MIO_UID
            FROM T_ZO_AP_Raum_AP_Ref_Mietobjekt 
            WHERE ZO_RMMIO_Status = 1 
            AND ZO_RMMIO_UID != @in_ZO_RMMIO_UID
            AND ZO_RMMIO_RM_UID = @in_ZO_RMMIO_RM_UID 
            AND ZO_RMMIO_MIO_UID = @in_ZO_RMMIO_MIO_UID 
            AND ZO_RMMIO_DatumVon = @in_ZO_RMMIO_DatumVon 
            AND ZO_RMMIO_DatumBis = @in_ZO_RMMIO_DatumBis 
        )
            SET @bIsDuplicate = 'true'

        RETURN @bIsDuplicate
    END


GO




ALTER TABLE [dbo].[T_ZO_AP_Raum_AP_Ref_Mietobjekt]  WITH NOCHECK ADD  CONSTRAINT [CheckNoDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt] 
CHECK  
(
    NOT 
    (
        dbo.fu_InsertCheck_IsDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt(ZO_RMMIO_UID, ZO_RMMIO_RM_UID, ZO_RMMIO_MIO_UID, ZO_RMMIO_DatumVon, ZO_RMMIO_DatumBis) = 1 
    )
)
GO


ALTER TABLE [dbo].[T_ZO_AP_Raum_AP_Ref_Mietobjekt] CHECK CONSTRAINT [CheckNoDuplicate_T_ZO_AP_Raum_AP_Ref_Mietobjekt]
GO

And here a test case:

CREATE TABLE [dbo].[T_ZO_AP_Raum_AP_Ref_Mietobjekt](
    [ZO_RMMIO_UID] [uniqueidentifier] NOT NULL,  -- <== PRIMARY KEY
    [ZO_RMMIO_RM_UID] [uniqueidentifier] NOT NULL,
    [ZO_RMMIO_MIO_UID] [uniqueidentifier] NOT NULL,
    [ZO_RMMIO_DatumVon] [datetime] NOT NULL,
    [ZO_RMMIO_DatumBis] [datetime] NOT NULL,
    [ZO_RMMIO_Status] [int] NOT NULL,
    [ZO_RMMIO_Bemerkung] [text] NULL
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

GO



/*
DELETE FROM T_ZO_AP_Raum_AP_Ref_Mietobjekt 
WHERE ZO_RMMIO_Status = 1 
AND ZO_RMMIO_RM_UID = '2007B6F5-9010-4979-AB39-00057DA353C0' 
AND ZO_RMMIO_MIO_UID = 'FFA177E9-971E-4500-805D-00116F708E7B'
*/


INSERT INTO T_ZO_AP_Raum_AP_Ref_Mietobjekt
(
     ZO_RMMIO_UID
    ,ZO_RMMIO_RM_UID
    ,ZO_RMMIO_MIO_UID
    ,ZO_RMMIO_DatumVon
    ,ZO_RMMIO_DatumBis
    ,ZO_RMMIO_Status
    ,ZO_RMMIO_Bemerkung
)
VALUES
(
     NEWID() --<ZO_RMMIO_UID, uniqueidentifier,>
    ,'2007B6F5-9010-4979-AB39-00057DA353C0' --<ZO_RMMIO_RM_UID, uniqueidentifier,>
    ,'FFA177E9-971E-4500-805D-00116F708E7B' --<ZO_RMMIO_MIO_UID, uniqueidentifier,>
    ,'01.01.2012' --<ZO_RMMIO_DatumVon, datetime,>
    ,'31.12.2999' --<ZO_RMMIO_DatumBis, datetime,>
    ,1 --<ZO_RMMIO_Status, int,>
    ,NULL--<ZO_RMMIO_Bemerkung, text,>
)
GO



INSERT INTO T_ZO_AP_Raum_AP_Ref_Mietobjekt
(
     ZO_RMMIO_UID
    ,ZO_RMMIO_RM_UID
    ,ZO_RMMIO_MIO_UID
    ,ZO_RMMIO_DatumVon
    ,ZO_RMMIO_DatumBis
    ,ZO_RMMIO_Status
    ,ZO_RMMIO_Bemerkung
)
VALUES
(
     NEWID() --<ZO_RMMIO_UID, uniqueidentifier,>
    ,'2007B6F5-9010-4979-AB39-00057DA353C0' --<ZO_RMMIO_RM_UID, uniqueidentifier,>
    ,'FFA177E9-971E-4500-805D-00116F708E7B' --<ZO_RMMIO_MIO_UID, uniqueidentifier,>
    ,'01.01.2012' --<ZO_RMMIO_DatumVon, datetime,>
    ,'31.12.2999' --<ZO_RMMIO_DatumBis, datetime,>
    ,1 --<ZO_RMMIO_Status, int,>
    ,NULL--<ZO_RMMIO_Bemerkung, text,>
)
GO

SELECT [ZO_RMMIO_UID]
      ,[ZO_RMMIO_RM_UID]
      ,[ZO_RMMIO_MIO_UID]
      ,[ZO_RMMIO_DatumVon]
      ,[ZO_RMMIO_DatumBis]
      ,[ZO_RMMIO_Status]
      ,[ZO_RMMIO_Bemerkung]
  FROM [T_ZO_AP_Raum_AP_Ref_Mietobjekt]