Novice question about MS SqlServer.

I have an application which uses what I call an "overloaded" table. By that I mean that it contains columns of relational key ID's that can relate to different tables depending on another definitive field in the table. For example, x1_ID relates the record to an Invoice header if the xntype field value is "CHARGE" or "PAYMENT" but if the xntype field value is "INVRECEIVE", x1_ID relates the record to a Purchase Order Header record.

This structure has worked well for me for several years in VFP but I have been told that it is not allowed in a SQL Server table. Have I been misinformed or have I been misusing this capability in VFP ?

Thanks,

Ken