Reference one foreign key to multiple primary keys in SQL Server 2014

Question

I have three tables in my database.

1. MedicalTest [MedicalTestID PK]
2. SportTest [SportTestID PK]
3. GeneralNeeds [GeneralNeedsID PK]

Inside GeneralNeeds there is ProcessID which needs to keep MedicalTestID and SportTestID GUID.

As soon as I insert an existing GUID from either tables I get "Conflict" error message which I believe it means the given GUID doesn't exist in the other table.

For example: If I insert the GUID from MedicalTest then it will tell me that the SportTest doesn't have the given GUID.

Is it possible to reference multiple keys to one column?

Answer 1

The design I'd recommend here is a table/sub-table solution. What that means is, introduce a 4th table, Test . The Test table just serves as a table that links all the different test types together. If you're familiar with Object Oriented Programming, think of it as a base type. So essentially, your ProcessID points to Test which then points to one of the specific test types (SportsTest, MedicalTest, WhateverTest). If you like, you could also include a Type in the Test table to help you know which type of test it is. There is a key thing here: In the MedicalTest and SportsTest table, the primary key (say MedicalTestID ) is also a foreign key that points to the TestID in Test . In this way you can use a single column in your GeneralNeeds because the reference is to a single table type, Test . Since Test and the corresponding MedicalTest or SportsTest would have the same primary key, you can easily do the joins you need to do the query.

Here is a sample diagram illustrating it:

Simple example: Say you have a MedicalTest with ID of 1 (let's forget GUIDs for a minute to make it easier to read) Then you'd also have a record in Test with an ID of 1. Then the ProcessID of 1 really points to the Test record which you could then join to the MedicalTest record.

If you're still confused let me know and I'll try to add a bit more detail but hopefully this gets you going in a direction that works.