sql server 2008 - Foreign key or link between part of column selection -

i have 3 tables in following setup

create table [dbo].[codevariable] (     [id] [int] null,     [code] [nchar](10) null,     [variable] [int] null ) on [primary]  create table [dbo].[proxy] (     [id] [int] null,     [description] [nvarchar](50) null,     [status] [bit] null,     [added] [datetime] null ) on [primary]   create table [dbo].[wall] (     [id] [int] null,     [description] [nvarchar](50) null ) on [primary] 

following values in tables table wall

1   basic wall 2   medium wall 3   advanced wall 

table proxy

1   small proxy true    2013-05-08 00:00:00.000 2   medium proxy    false   2013-05-08 00:00:00.000 

table codevariable

1   proxy       1          2   proxy       2          3   wall        1          4   wall        2          5   wall        3       

owke issue facing, if want insert lets new line in proxy. have id 3, need make sure id 3 exists in codevariable under code proxy!

without foreign key there no check if code exists in code variable.

i have tried foreign keys without success. how can create link between codevariable table on columns code , variable towards table proxy , table wall.

i can created index on code , variable unique. u cannot link foreign key it.

i using sql 2008

thanks

one way change table definitions, foreign key constraints can enforced.

use composite primary key (codeid, codetype) table codevariable (renamed code), codetype can take 2 possible values, either 'p' or 'w'.
(the code had used instead of codetype preferred narrower column keys (primary , foreign) used in indexes.
code converted computed column):

create table [dbo].[code] (     [codeid] [int] not null,     [codetype] [char](1) not null,     [codename]                               -- computed column          case codetype when 'p' 'proxy'                        when 'w' 'wall'          end,     constraint code_pk         primary key (codeid, codetype),     constraint codetype_ck         check (codetype in ('p', 'w')) ) ; 

in 2 other tables, codetype added well, (codeid, codetype) can defined both primary , foreign key:

create table [dbo].[proxy] (     [proxyid] [int] not null,     [codetype] [char](1) not null default 'p',     [description] [nvarchar](50) null,     [status] [bit] null,     [added] [datetime] null,     constraint proxy_pk         primary key (proxyid, codetype),     constraint code_proxy_fk         foreign key (proxyid, codetype)         references code (codeid, codetype),     constraint codetype_proxy_ck         check (codetype = 'p') ) ;   create table [dbo].[wall] (     [wallid] [int] not null,     [codetype] [char](1) not null default 'w',     [description] [nvarchar](50) null,     constraint wall_pk         primary key (wallid, codetype),     constraint code_wall_fk         foreign key (wallid, codetype)         references code (codeid, codetype),     constraint codetype_wall_ck         check (codetype = 'w') ) ; 

sql-fiddle