Date: Sat, 24 Sep 2005 23:34:15 -0400
From: Ferindo Middleton Jr <fmiddleton@verizon.net>
Subject: redundancy in CHECK CONSTRAINTs
To: pgsql-sql@postgresql.org
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I have the following table:

CREATE TABLE gyuktnine (
     id               SERIAL,
    intsystem      INTEGER NOT NULL REFERENCES yuksystems(id) CONSTRAINT 
int_cannot_equal_ext
                       CHECK (intsystem != extsystem),
    extsystem     INTEGER NOT NULL REFERENCES yuksystems(id) CONSTRAINT 
ext_cannot_equal_int
                        CHECK (extsystem != intsystem), 
    PRIMARY KEY (intsystem, extsystem)
);

the intsystem and extsystem fields both have a check constraint on them 
which preventing any one record from having values in which they are 
equal. There is also a primary key. Is this redundant? Do only one of 
them really need this constraint? Or does it not really matter. I'm 
concerned about using constraints like this and have redundant checks 
built in slowing down my db.

Ferindo