Add Foreign Key to information_schema.tables

Question

I would like to have a table with a column that references another table (not reference a column in another table).

I'm using SQL Server 2008 R2

So i have tblA, tblB and tblC. tblA has a colum "OtherTable" of varchar. I want a Foreign Key Contraint that only allows the values "tblA", "tblB" or "tblC" as values in this column.

I tried it with a normal Foreign Key

ALTER TABLE dbo.tblA
ADD FOREIGN KEY (OtherTable)
REFERENCES information_schema.tables(TABLE_NAME);

And got the following Error:

Msg 1767, Level 16, State 0, Line 1

Foreign key 'FK__tblA__Tabel__27CED166' references invalid table 'information_schema.tables'.

Msg 1750, Level 16, State 0, Line 1

Could not create constraint. See previous errors.

I also tried it with a Check Constraint

ALTER TABLE dbo.tblA
ADD CHECK (OtherTable IN (SELECT TABLE_NAME FROM information_schema.tables));

But this also gives me an Error:

Msg 1046, Level 15, State 1, Line 6

Subqueries are not allowed in this context. Only scalar expressions are allowed.

Is it possible to have this kind of Constraint?

Answer 1

Information_schema.tables是一个视图，您不能在外键中引用该视图。

Answer 2

Build your own list of allowed values (user-def table) and reference it. Better choice is to store readable value which says "why" you have to look for data in some other table eg record type . And check out other questions about polymorphic data structures - seems to me you are building something similar.

And you should beware of FK-referencing system tables. Those tables are not parts of your application.