In SQL Server 2008 and given TableA(A_ID, A_Data), TableB(B_ID, B_Data), and ViewC(A_or_B_ID, A_or_B_Data), is it possible to define TableZ(A_or_B_ID, Z_Data) such that Z's A_or_B_ID column is constrained to the values found in ViewC? Can this be done with a foreign key against the view?
If you really need A_or_B_ID
in TableZ, you have two similar options:
1) Add nullable A_ID
and B_ID
columns to table z, make A_or_B_ID
a computed column using ISNULL on these two columns, and add a CHECK constraint such that only one of A_ID
or B_ID
is not null
2) Add a TableName column to table z, constrained to contain either A or B. now create A_ID
and B_ID
as computed columns, which are only non-null when their appropriate table is named (using CASE expression). Make them persisted too
In both cases, you now have A_ID
and B_ID
columns which can have appropriate foreign
keys to the base tables. The difference is in which columns are computed. Also, you
don't need TableName in option 2 above if the domains of the 2 ID columns don't
overlap - so long as your case expression can determine which domain A_or_B_ID
falls into
(Thanks to comment for fixing my formatting)