Question

Consider we have two tables ProductType and ProductSizeGroup as below

ProductType

Id 
Name
MaleSizeGroupId
FemaleSizeGroupId
ChildSizeGroupId

ProductSizeGroup

Id
Name

Each of MaleSizeGroupId, FemaleSizeGroupId and ChildSizeGroupId fields should be FKs to ProductSizeGroup.Id.

I add one using the following statement:

ALTER TABLE [dbo].[ProductType]  
WITH CHECK ADD CONSTRAINT
    [FK_ProductType_ProductSizeGroup_Male] FOREIGN KEY([MaleGroupId]) 
    REFERENCES [dbo].[ProductSizeGroup] ([Id])

This works fine. I try to add the next using

ALTER TABLE [dbo].[ProductType]
WITH CHECK ADD CONSTRAINT
    [FK_ProductType_ProductSizeGroup_Female] FOREIGN KEY([FemaleGroupId]) 
    REFERENCES [dbo].[ProductSizeGroup] ([Id])

But I get the error:

The ALTER TABLE statement conflicted with the FOREIGN KEY constraint “FK_ProductType_ProductSizeGroup_Female”. The conflict
occurred in database “dbname”, table “dbo.ProductSizeGroup”, column
‘Id’.

So there is conflict.. but what conflict? What should I be looking for?

Answer 1

That just means: there are rows in your table ProductType that have values in the FemaleGroupId column which do not exist in the referenced table (ProductSizeGroup).

It’s not a problem per se – you can totally have multiple columns going from one table to another.

The problem is with the existing data – you have data in there that doesn’t live up to that FK constraint. Fix that data and you should be fine.

To find those offending rows, use a query like this:

SELECT * 
FROM [dbo].[ProductType]
WHERE FemaleGroupId NOT IN (SELECT DISTINCT Id FROM [dbo].[ProductSizeGroup])

That will list all offending rows – update their attribute and get going again!