Date: Fri, 2 Sep 2005 15:23:56 +0200
To: pgsql-sql@postgresql.org
Subject: not sure about constraints
Message-ID: <20050902132356.GD10284@mail.librelogiciel.com>
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From: Jerome Alet <alet@librelogiciel.com>

Hello,

I've got 4 tables :

CREATE TABLE tableA (id SERIAL PRIMARY KEY NOT NULL,
                     blahA TEXT);
                     
CREATE TABLE tableB (id SERIAL PRIMARY KEY NOT NULL,
                     blahB TEXT);
                     
CREATE TABLE tableC (id SERIAL PRIMARY KEY NOT NULL,                     
                     ida INT4 REFERENCES tableA(id),
                     idb INT4 REFERENCES tableB(id),
                     blahC TEXT);
                     
CREATE TABLE tableD 
    (id SERIAL PRIMARY KEY NOT NULL,                     
     ida INT4,
     idb INT4,
     blahC TEXT,
     CONSTRAINT checkAB FOREIGN KEY (ida, idb) REFERENCES tableC(ida, idb));
                     
Is the definition of tableD sufficient, or should I do it this way 
instead : 

CREATE TABLE tableD 
    (id SERIAL PRIMARY KEY NOT NULL,                     
     ida INT4 REFERENCES tableA(id),
     idb INT4 REFERENCES tableB(id),
     blahD TEXT,
     CONSTRAINT checkAB FOREIGN KEY (ida, idb) REFERENCES tableC(ida, idb));
                     
which looks superfluous to me.                     

???

Thanks in advance

Jerome Alet