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From: Tim Landscheidt <tim@tim-landscheidt.de>
Subject: Re: FOREIGN KEY Reference on multiple columns
Date: Wed, 24 Sep 2014 18:02:34 +0000
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"Weiss, Jörg" <J.Weiss@dvz-mv.de> wrote:

> I mean b must equal to c1  in the "other_table" where c2 has a certain value (for example c2 ).

> For my first example:
> CREATE TABLE parm
> (
>   complex varchar(20) NOT NULL,
>   para varchar(50) NOT NULL,
>   sort int4 NOT NULL DEFAULT 10,
>   value varchar(50) NULL,
>  CONSTRAINT parm_pkey PRIMARY KEY (complex, para, sort)
> )

> Table user
> CREATE TABLE user
> (
>   name varchar(20) NOT NULL,
>   type integer NULL
> )
> In this case "type" of table user must equal to "value" of table "parm" and "para" must be "login_user" (for example)

> [...]

You can achieve that by duplicating the para column to the
table user, adding a foreign key that matches both columns
to table parm and checks in table user whether para is
"login_user".  That doesn't work for NULLable columns,
though.

Tim


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