Question

I have the following table:

CREATE TABLE [dbo].[EntityAttributeRelship](     [IdNmb] [int] IDENTITY(1,1) NOT NULL,     [EntityIdNmb] [int] NOT NULL,     [AttributeIdNmb] [int] NOT NULL,     [IsActive] [bit] NOT NULL CONSTRAINT [DF_EntityAttributeRelship_IsActive]  DEFAULT ((0)), CONSTRAINT [PK_EntityAttributeRelship] PRIMARY KEY CLUSTERED  ([IdNmb] ASC) WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]) ON [PRIMARY] 

A portion of the data in the table looks like something this:

IdNmb    EntityIdNmb    AttributeIdNmb  IsActive 1        22             7               0 2        22             8               0 3        22             9               0 4        22             10              1 

I want to add a constraint to make sure that no one adds or updates a record to have IsActive = 1, if there is already a record for the EntityIdNmb where IsActive = 1.

How do I do this?

Answer 1

If you are using SQLServer you can create a clustered indexed view.

CREATE VIEW dbo.VIEW_EntityAttributeRelship WITH SCHEMABINDING AS SELECT EntityIdNmb  FROM dbo.EntityAttributeRelship WHERE IsActive = 1 GO  CREATE UNIQUE CLUSTERED INDEX UIX_VIEW_ENTITYATTRIBUTERELSHIP    ON dbo.VIEW_EntityAttributeRelship (EntityIdNmb) 

This ensures there’s only one EntityIdNmb in your table with IsActive = 1.